"It was an opponent Nanoha wouldn't have had any problem protecting her allies from or defeating if she had been her usual self. But the strain of overexerting herself made Nanoha less capable, and her body slowed down at a crucial moment. The result... was this."
A type of fandom-based Author's Saving Throw, this is the specific rationalization that a character suffering from The Worf Effect or a Curb-Stomp Battle did so only because something (artificially) undermined their performance. The insinuation, of course, is that it probably wouldn't have happened this way under "normal" circumstances.
This is often used within fandom, and can be a satisfying answer for fans bothered by the outcome of the battle or use of the trope itself. As the 'flu' is generally pulled from something within the story, explicit or otherwise, it does not necessarily require a blatant Retcon or Canon Discontinuity — the event itself is still treated as canonical. Note, however, the new reason may not officially be, except as a passing Ascended Fanon by some writers.
Whether or not a later matchup is provided becomes irrelevant. If enough ire is raised from using the Worf Effect, a later matchup may be specifically avoided to dodge any mention of it at all. On the other extreme, the response to the trope may be too loaded with Take That overtones not to come off as petty. In contrast, a well-written Evasive Fight Thread Episode often includes 'flu' logic in an effort to quell any complaints about the match-up. Essentially the "Power Seep" part of Power Creep, Power Seep.
This Flu is also often exploited by a nasty Big Bad Wannabe in order to have a shot to kill those powerful people, through luck mostly. Of course, defeating those who had flu doesn't mean you are that trope. With planning and exploiting this 'Flu', one can avoid being labeled of that trope.
A type of Drama-Preserving Handicap. Compare Actually a Doombot. Contrast Handicapped Badass when they managed to win despite their flu. This is the opposite trope to in his best condition.
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Anime and Manga
In Bleach, Ichigo's poor performance in his battles against Ulquiorra and Yammy, as well as his first battle against Grimmjow, is attributed to his difficulty suppressing his inner hollow. When he does manage to control his inner hollow, he is still unable to defeat Grimmjow the second time, and loses to Ulquiorra the first time he fights him in Las Noches.
In the Arrancar arc, Hitsugaya, Rangiku and Renji are losing to their Arrancar enemies, but then they get permission to release their Power Limiters, and easily defeat their foes. Being limited to 1/5 of one's power is a pretty crippling handicap.
Ichigo when confronted by the Quinto Espada, Nnoitra Gilga, gets easily owned, then gets bored and leaves the ass-whooping to his Fraccion, Tesla. It should be noted that Ichigo had a grueling battle against the Sexta Espada, Grimmjow Jaegerjaquez (who also got owned by Nnoitra,) in which he barely defeated him. This is shown when he took on Ulquiorra again, and was a match for him, until he had to release (Ulquiorra lost, but Ichigo doesn't consider his Superpowered Evil Side laying the smackdown on him a fair fight).
The entire Bount Arc is this trope. Every Soul Reaper who comes to Earth can only use a fraction of their power, and Ichigo has to relearn Bankai for some silly reason. Even the Bount enemies don't reach full power until they travel to the Soul Society.
In the Invasion Army arc, Ichigo's power was failing after having used it all up fighting Aizen. So of course he was coming into this new dilemma already handicapped.
In the Lost Substitute arc, it's revealed that Ichigo's reiatsu was being surpressed by his substitute badge, explaining his poor performance in the Arrancar Invasion arc.
Early on, Renji's bankai was destroyed and repaired after a fight with Byakuya. It has been recently revealed that a bankai that's been broken never retains its original full strength and potential, hence his lackluster win record.
In the final arc, the reason Ichigo's power fluctuates so much is revealed: the "Old Man" that embodies his Quincy powers always suppressed Ichigo's Shinigami powers in a vain attempt to keep him from becoming a Shinigami. By the time he reveals this, he has already grown proud of Ichigo and he finally allows Ichigo to use his full power. Seriously, how many power limiters does this kid need?
In chapter 580, Zaraki Kenpachi is defeated with two blows by the Femritter. One of them is surprised that he was even able to move in the first place since he had just sustained massive injuries fighting a Reality Warper.
In the past, Isshin Shiba would have been able to defeat the Proto-Arrancar White with ease if he could use his Bankai, but Aizen snuck up and slashed him across the back, rendering him unable to.
In the anime Berserk, Casca actually loses and needs rescuing from her first battle with Adon Corbowitz. While tending to her Guts notes blood between her thighs and comments to himself how it must be hard for a woman mercenary. The next time she and Adon meet, the beatdown goes the other way.
It's also a Chekhov's Gun, as she's seen being 'out of it' earlier. Furthermore, as in case the viewer doesn't get it, Adon says, when being beat down: "YOU HAD PMS!?"
Luffy and the rest of the Straw Hats are initially unable to defeat the CP9, and while they are not yet using the techniques they use to defeat their opponents in later battles, Nami suggests that they weren't fighting at their full potential because they were still unsure whether Robin had betrayed them. Once they realize that she did what she did for their sake, they are able to fight to their full power to rescue her (Strangely enough, Sanji knows Robin's reasons and still is unable to defeat Blueno, but later defeats the far more powerful Jyabura). Luffy also admits he wasn't at his fullest because he wasn't full and just fought Wanze, whow as a relatively weak enemy but managed to thrash Sanji a fair amount before he started using knives.
Earlier in the manga, Sanji was wounded by Pearl and nearly lost to Gin.
In the Skypiea arc, Luffy, Zoro and Sanji are unable to fight well against Wiper because they have not adapted to Skypiea's higher elevation and thinner atmosphere. Luffy manages to get over this by the time he fights the White Berets, and throughout the rest of the arc, there is no suggestion that the characters are fighting at anything less than their full potential.
The Straw Hats exhaust themselves fighting the first Pacifista on the Sabaody Archipelago, making them easy pickings for Sentoumaru, Kizaru, Kuma and another Pacifista.
Kuma seems to be a fan of this trope, considering that he's beaten the Strawhats twice, and both times he confronted them right after they'd fought a major, exhausting battle.
Luffy's somewhat underwhelming (Haki aside) showings during the Kuja and Marineford battles are at least partially attributed to having to deal with the Kizaru/Kuma/Sentoumaru/Pacifista gangstomp the day before in the previous case and nearly dying against Magellan and being kept running on sheer willpower and hormone doping in the latter case. Of course, a lot of it has to do with the fact that the major players are all Warlord of the Sea class, at least, but the Luffy at Marineford didn't seem to be operating at the same caliber as he did against the likes of Rob Lucci and Gecko Moria, and actually had to be doped again near the end of the battle.
This was the primary reason Franky was struggling against Fukurou, despite having previously overpowered Blueno; As he was lacking in Cola, his attacks were decreased in effectiveness and power. Once he got his cola back...
Seriously, many of Zoro's battles had him at some sort of disadvantage or not at his full potential. In the battle with Cabaji, he was already injured from Buggy's earlier attack. When fighting Hachi, he was still recovering from his wounds from his fight with Mihawk and had a fever on top of that. He had difficulty with Mr 1 since Mr 1's body can become steel, something Zoro couldn't cut at the time. During the Davy Jones game, he wasn't able to use his swords due to the rules. He only had two swords with him during the fight against Ryuuma. And against Oars, he was still getting used to his new sword Shuusui. With Kuma, he had taken damage from Ryuuma and Oars over the night. With the Flying Fish Riders and with the Pacifista, he was hampered down from his injuries from Thriller Bark, along with Luffy's pain that was transferred to him.
Violently defied during his fight with Cabaji, who was targeting his earlier wound from Buggy. Zoro, mindful of his goal to be the best swordsman alive, proceeded to cut open the wounds, making them much worse. Cabaji believed that to be giving him an out, as Zoro could use the injury as an excuse for a loss. Zoro refutes that, saying that if he lost to someone like Cabaji with such a "minor" injury, he may as well give up on his dream altogether. He then hands Cabaji his ass.
Whitebeard, the man considered the equal to Roger at his peak, went into the Marineford war suffering from illness, old age and injury. While his raw power and toughness still impressed, many people noted he was nowhere near the top of his game, causing him to tank attacks that he could have either blocked or evaded. Taking all those attacks did eventually kill him.
Though considering how much damage his rampage caused, it's made people wonder how powerful he was when he was in his prime - and how powerful Roger was when he was still alive.
This was the case with Trafalgar Law. Before the Time Skip he was too weak to stand up to Vergo, and was absolutely terrified of him. After it, it seems the situation has not changed, with Vergo curb-stomping him twice. However, this was mainly due to having Law's heart. Once Smoker got Law his heart back, Law proceeded to curb-stomp Vergo in his most powerful form with one slash, cutting not only Vergo but also the entire laboratory as well.
Happens to Law again in the Dressrosa arc. By the time he fights Donquixote Doflamingo one-on-one, he had to fight both Doflamingo and Admiral Fujitora at the same time, then protect Caesar and the Straw Hats from Doflamingo. He was undoubtedly exhausted by that point, and it doesn't help that his devil fruit abilities are explicitly stated to rely on his stamina. As an end result, he suffers a very bad Curb-Stomp Battle at Doflamingo's hands.
One scene in Episode 52 of the Naruto Shippuden anime (which doesn't appear in the manga) suggests that Naruto and Sakura faired poorly against Sasuke in their first meeting with him after the timeskip because of their wounds from their previous battle (although they do realize that Sasuke has gotten far more powerful). Yamato is also holding back, not wanting to injure Sasuke too much, but just after he decides to get serious, Orochimaru leaves with Sasuke.
This is the only reason why Orochimaru was able to beat Hiruzen Sarutobi, the Sandaime Hokage. Hiruzen was way past his prime by the time of their fight and even the simple use of the Kage Bushin technique ate away at his lifespan. Orochimaru even said that had this been just ten years before, even with the Edo Tensei Hokages, Hiruzen would have won then. But...since Hiruzen was in old age, the best he could do was a tie with a Taking You with Me jutsu against Orochimaru and the Edo Hokages.
In the manga, Naruto was still suffering from his Four-Tailed Form's side effects. He was, at best, half power when he finally encountered Sasuke (even Orochimaru commented when they fought again, Naruto wasn't doing nearly as well before). Sakura, likewise was still suffering from the poisonous wound that she had gotten from the Kyuubi's tail swipe. Only Yamato and Sai were at full strength.
Before the Time Skip, during the Chunnin exam tournament, Jiraiya notices the chakra-blocking seal that Orochimaru had placed over Naruto's Kyubi-containing belly-button seal, and realizes it prevented Naruto from channeling properly. Once he removed it, Naruto was able to instantly master the water-walking technique he had been struggling with before. And it might also explain Naruto's rather lackluster performance against Kiba — Naruto previously never needed any distractions or significant pauses in a fight to create Shadow Clones. Of course, Naruto himself never seemed to notice his own difficulties...
Orochimaru has had to been sick or weak at the time for both Uchiha Itachi and Uchiha Sasuke to defeat him. When he faced both, for example, his body was rejecting him both times, and he couldn't kill either of them (needing their bodies for Grand Theft Me). Its even pointed out later that the only reason why Sasuke beat Orochimaru in the first place is because Sandaime Hokage's Shiki Fujin still sealed his arms, thus robbing him of his ninjutsu.
Tsunade's first appearance has her using then-current Big Bad Orochimaru like a paddleball. The only reason Orochimaru did not bust out far more powerful moves for the fight was because had previously lost the use of his arms (and thus, most of his jutsus). Jiraiya was likewise disabled thanks to a drug Tsunade slipped into one of his drinks earlier on. Tsunade as well suffered some early damage due to her entirely psychological weakness to blood, making her use her trump card on a healing power and, less memorably, as years out of practice. If the Sannin were at their top form during the fight the others there would've been useless and the battle would've dwarfed even the epic rumble that it was and likely not be quite as one-sided.
The Sound Four were all capable of holding off multiple ANBU agents in their first appearance, but all lost to genin later on. However, this (and the fact that the Konoha genin caught up to them in the first place) was at least partially because they had exhausted themselves when they ran into two Konoha jonin and had to activate their cursed seals just to get away with Sasuke's body unharmed. Even with this, Sakon and Tayuya still almost won their fights and only lost because of the sand genin's interference.
Said jonins were exhausted themselves, because they ran into the Sound Four while en route back to the village, after a mission.
Especially true with Kimimaro, who was literally seconds away from killing Gaara and Rock Lee when his illness causes him to die. Given that he was able to defeat the sound four all at once and was able to move with sheer willpower, it is especially evident.
Played with in Sasuke's battle with Itachi. Not only is Itachi in terrible shape (basically, using the high level Sharingan techniques means Cast from Hit Points, with the negative that a night at the Inn does NOT fix you right up), he's damn near blind, holding back, and was actually trying to let him win and yet he still utterly dominates Sasuke, who is in top form. Sasuke only survives because Itachi dies at the end.
To be fair though Itachi only 'dominated' when Susano'o came into play since Sasuke had no knowledge of said technique, thus no counter unlike having counters to Amaterasu with Oral Rebirth or Tsukuyomi with his Sharingan mastery and rage. Even Itachi complimented Sasuke's power, and if not for Susano'o Kirin would have wiped Itachi off the face of the map.
Pain versus Naruto could have been much more one sided with the odds heavily against Naruto had it not been for the fact that Pain was trying to capture Naruto, not kill him. It also didn't help that he'd just finished fighting and leveling a village, and his most powerful body had its powers disabled at the start of the fight.
Sasuke's poor performance against Killer Bee is accredited to him not being fully recovered from his fight with Itachi.
Danzo only lost to Sasuke since he was unable to use Shisui's eye and was holding back power to fight Tobi, who was the more dangerous opponent.
And going back allllll the way, Naruto's crappy abilities with chakra control are implied to be due to the Kyuubi's chakra inside him. Once he started getting his jutsu under control, he was learning jounin level skills (albeit in a wasteful manner — thank the Sage of Six Paths that he's got enough chakra to burn) and a technique that requires a practically impossible level of chakra control.
It's almost a necessity in the Naruto universe; the majority of techniques and strategems are actually fairly accurate for how a ninja with quasi-magical powers would be: an attack, preferably a sneak attack, that tends to be somewhere between a One-Hit Kill and ridiculously excessive. The fights would be a lot shorter and the action a lot less interesting if they lasted one panel/minute EVERY single time.
Naruto himself suffered this during the War Arc. Against Nagato and Itachi, he was starting to run on empty for his Nine-Tailed Chakra Mode due to using it all night, fighting the Raikage, then creating 13 clones to help on several battlefields. When he attempted to create a clone to find Kabuto, his Chakra Mode disappeared and he was left exhausted. Then during the fight with Tobi, he couldn't use his superior speed and barely used any jutsu's against Tobi's paths due to being so completely exhausted from his previous fights. Its only after getting Kurama's partnership he's able to truly pull a Heroic Second Wind. Even after his Biju Mode runs out, he's completely recharged but he still uses his Chakra Mode conservatively against Tobi so he isn't lured into the same trap he was before.
Sakura's apparently been charging her Yin Seal for the past three years.
Madara and Hashirama as Edo zombies both lacked some/most of their power due to their summoner being too weak to bring them back properly, which makes it possible for living people to defeat them.
Played with In the first arc, Goku eventually uses up his strength fighting with Yamcha, who then powers into some sort of Unstoppable Rage, then the fight gets interrupted by Bulma.
Also happens when Goku loses to King Piccolo's minion Tambourine, but only because Goku was exhausted from fighting in the 22nd Tenka'ichi Budokai. Tambourine is confident he can win again in the rematch, but things don't go so well for him.
Lordgenome of Tengen Toppa Gurren Lagannwasn't fighting anywhere close to his real potential during his fight with Simon, and he still would have won if he had not underestimated Simon's determination. A thousand years of boredom had dulled his edge considerably, as he proved during the final episode.
Even more true considering that according with his backstory revealed in the Parallel Works 8, Lord Genome turns against his own comrades in the name of the Anti-Spiral effectively taking down a LEGION OF SPIRAL WARRIORS all by himself, it's more or less stated that Genome, at the time, have the power to defeat the anti-spirals and end the war if he knew what to do but he was convinced and scarred by the truth of the Spiral Nemesis.
Similar to the Super Robot Wars example further down the page, Mahou Senki Lyrical Nanoha Force gives this treatment to Signum by way of depriving her of the equipment needed to fight against the Hückebein. Signum goes into her battle with Cypha lacking the countermeasures necessary to neutralize her opponent's Mage Killer abilities, and as a result only manages to hold her own until Cypha gets serious. Double points here because before this, Signum had never been defeated onscreen by any of the other characters.
Later on Signum inverts this instead. She did wake up and has gotten more proper equipment, but she has one more handicap: That injury was very life-threatening that she could end up crippled for life. When she instantly issues a rematch with Cypha, you expect that she'd lose out again or at best only manages to get even due to the injury. What happens was that in a single chapter, Signum completely beat the crap out of Cypha to the point she had to retreat.
Nanoha's overexerting herself resulted in her getting injured and almost crippled while on a mission, as Shamal points out in the above quote.
The Wolkenritter are less at an advantage over Nanoha and Fate's group because they have sworn not to kill anyonein their quest to save Hayate. Despite managing to fight off Signum until she retreats or outside forces interfere, Fate loses most of her sparring matches against Signum in the period after A's.
Prior to his first battle with Mukuro, Hibari from Katekyo Hitman Reborn! literally had been injected with a flu, causing him to get curb-stomped despite being at least Mukuro's equal in fighting prowess.
Ash's Grovyle from Pokémon evolves into Sceptile...into the worst possible moment, when he was heartbroken. Somehow, this causes Sceptile (a powerful Pokémon in its own right) to be unable to use its attacks, rendering it useless for a couple of episodes.
Ash's Pikachu gets a taste of this in the very first episode of the Unova saga. An encounter with Zekrom, one of Unova's Legendaries, overloads Pikachu's electricity-storing capability and thus renders it unable to use Electric-type attacks. Ash finds this out the hard way when the 'Chu gets trounced in a battle with a trainer who had, mere minutes earlier, received his first Pokémon.
There was, however, that one occasion in the Hoenn saga where it was actually used as an advantage, Applied Phlebotinum caused Pikachu to strike a fever, which also gave him an insane power up, leading up to Ash easily defeating Wattson.
"Charizard Chills" has the title Pokémon critically frozen after battle with a Poliwrath. His respect as well as loyalty for his trainer returned after Ash spent all night trying to thaw him out.
Later, he also suffers a wing injury during the battle against the Johto gym leader Faulkner, giving him a little bit of trouble against the leader's Pidgeot.
Most of the time Charizard loses a battle it's treated this way, examples include the losses against Dusclops (where has was holding a Idiot Ball) and Blaziken (because Ash had no knowledge of what a Blaziken was).
In Pokémon Special, Petrel claims that he had an easy time defeating Lance, easily one of the most powerful trainers in the world. Turns out that Petrel disguised himself as Yellow, the one person who Lance is afraid of, throwing him off his game.
Digimon Savers: In one episode, one of Masaru's punches breaks SaberLeomon's tooth. This wouldn't be out of character for him except that an earlier attempt to punch SaberLeomon had significantly less effect, and prior to the second attempt SaberLeomon had just taken a Gizumon blast, severely weakening him to the point when an Ultimate level Digimon could blow him up.
In the Tales of Symphonia manga, Lloyd claims that Kratos lost his last fight with him because he was still suffering from the wound he received protecting him from Yuan.
In Tokyo Mew Mew, Ichigo gets attacked by Kisshu in Episode 17 while she's sick, resulting in her being unable to defend herself and the Blue Knight appearing for the first time to save her.
Muhyo takes a long time to recover his tempering after a sentencing, so when a problem arises soon afterward, he's often unable to intervene immediately. As such, after the group defeats Face-Ripper Sophie, only for Rio to reveal herself as a traitor and attack them, they spend much of the battle retreating, and must brew Muhyo a dangerous potion to help him get his tempering back before they can effectively fight back.
In Tegami Bachi, during the infiltration of Honey Waters, Niche drinks some of the poisonous water that is the village's namesake. It doesn't take effect immediately, but when the villagers pin down Lag and Connor, Niche is only able to defeat Lag's attackers before being paralyzed from the poison, resulting in her and Connor being captured and Lag barely escaping.
Rurouni Kenshin: One of the reason Kenshin easily fell to Shishio in the first part of their battle was because he had already gone through battles with Aoshi and Sojirou. Both opponents were considered near or at Kenshin's level, so it would be a miracle for him to even be able to stand up to Shishio. This trope extended to Kenshin's allies as well; Saitou, Sano and Aoshi were unable to even hurt Shishio due to their previous injuries.
Shishio is actually concerned about whether or not this is fair, but Kenshin reminds him that it counteracts his own handicap, his lack of sweat glands which eventually set him on fire and burn him up from within. Shishio also plays with the trope, since it's implied that the extra heat energy his body produces makes him stronger somehow and he can literally kill someone by touching them long enough. Oddly enough, he doesn't use this as a weapon.
Medaka Box: Zenkichi's victory against Munakata is slightly downplayed, as despite his abnormal desire to kill, he was actually actively suppressing it.
Black Star's failure to use Soul Menace against Kid is actually a product of his inability to deal with the worfing that he's noticed he was being subject to. And THOSE losses were caused by him losing confidence in himself for not being able to master Shadow Star.
In Gundam SEED Destiny, when Athrun brought up how Shinn had defeated Kira, Kira admitted to being "distracted" because he was "unsure" if he should be fighting ZAFT or not.
In the Ninja Scroll movie, Dakuan reveals to Jubei that his victory over the monstrous Tessai wasn't wholly due to Jubei's considerable skill. Tessai had been poisoned when he tried to rape Kagero since Kagero is a Poisonous Person.
In The Prince of Tennis, Shinji and Kamio are spectacularly losing a doubles match and their coach/captain Tachibana is shocked as to why they're doing that badly. Jerkass Akutsu shows up and reveals that he knows why: he saw how the taxi that Kamio and Shinji were travelling in was involved in a crash. Tachibana calls off the match and is upset at the two... but not for having to pull them out, but because they didn't tell him that they were injured.
Tezuka is a frequent victim of this. Despite easily being one of the best players in the series, his arm injury has impeded his performance in pivotal moments, notably against Atobe and Sanada.
In the Nirvana arc of Fairy Tail, Jellal Fernandez, one of the most characters in the setting, is taken out off-panel by Midnight. Erza thinks to herself that this is because Jellal hadn't fully recovered from waking up from his coma.
Later, Ultear manages to defeat the Black Wizard Zeref, who had previously been talked up as one of the most powerful and dangerous wizards of all time. Zeref comes back later and explains that, as his magic is meant for causing grievous harm, he can only use it to his full extent when he's willing to kill his opponent, which he then proceeds to proove.
During the Makaiju/Doom Tree Filler Arc of Sailor Moon R Usagi watches in horror as her Moon Tiara Action attack powers down in mid-flight, leaving her a crying confused mess when the other Senshi come to the rescue. When a subsequent battle not only has this happen again, but also destroys her original brooch and strands her and Luna in another dimension, Usagi comes to realize the reason of this happening is because her head wasn't in the game: she didn't want to be Sailor Moon anymore and, because of it, it was affecting her powers. It takes a pep-talk with the spirit of Queen Serenity and a new brooch to get her back in the game.
In episode 96 of Sailor Moon S Makoto has her pure heart stolen. Then she and Uranus go head-to-head. Many fans saw Uranus' subsequent one-hit-knock-out of Jupiter to be pretty unfair and pointless except to show how SUPER-AWESOME Uranus is. However, the fact that Jupiter did just have her pure heart literally ripped out of her is a good reason that she may not have been up to snuff.
A recurring phenomenon in Holyland. When Yuu or whoever's heart is not in it, their fighting ability takes a large drop.
Cure Moonlight in HeartCatch Pretty Cure! has this leading to why she's taken out of action for 3/4ths of the series. It's kinda hard to fight with your head straight when you see your fairy partner blow up and disintegrate in front of you.
In Sword Art Online, Kirito has a kendo sparring match with his sister, a champion-level swordswoman. They fight pretty evenly until she wins. She points out that as his muscles had severely atrophied from being in a two-year coma (the match happens roughly a month after he woke up), had he been at full strength, he would have easily won.
Not to mention that Kirito was trying to use the sword fighting style he learned in the game during a real world fight, where he didn't have a computer aiding him with the moves, or nigh superhuman speed, strength, and reflexes to pull off the moves.
Magic users in Slayers lose a lot of power when their health is compromised, which is especially problematic for sorceresses during that time of the month. This makes it much easier for Zelgadis to capture Lina during an early story arc.
Toki in Fist of the North Star suffers from severe radiation poisoning which saps his strength. Technique-speaking he's the best user of Hokuto Shinken in the series, and Raoh and Kenshiro both know he'd have been the successor of the style if it hadn't been for his illness.
In Magic Knight Rayearth, Ascot takes out Hikaru and Fuu at the Water Shrine when he summons a fire beast—not only will Hikaru's magic strengthen it, Fuu's will as well because it's wind-based and you do not want to add oxygen to a fire.
In the big DC vs Marvel crossover, one fight that attracted particular opprobrium from fans was Lobo—a character who can go toe-to-toe with Superman and at the time could regenerate from a single drop of blood—losing to Wolverine (who at the time didn't even have his adamantium skeleton, though his healing factor was significantly boosted as a result). This was explicitly down to Popularity Power—the results were voted on by fans—but the match-up was so uneven the writers had to have Wolverine's victory take place off-panel. A little while later Lobo mentioned that he'd actually been bribed by "some bald guy" (presumably Professor X) to take a dive in the fight.
One of the more famous events in the history of the X-Men is the battle for leadership of the team between Cyclops and Storm - who at the time had no powers. Storm won by stealing Cyclops' visor. Without the control of the visor, any attempt to continue fighting would've run the risk of killing Storm (or any of the audience), so he gave up. Several years later, Cyclops' ex-wife Madelyne Pryor announced that she'd used her psychic powers to make Cyclops lose. This is a relatively easy Retcon since Cyclops spent much of the fight distracted by a major argument he and Madelyne had just been having, so to say he didn't exactly have his mind on the battle was very easy to change into a result of Madelyne's direct influence.
Played in advance in the Superman vs Predator mini-series. Under normal circumstances the Predators would have posed no threat whatsoever - so the story had Superman catch alien flu just as he arrived in the jungle where they had landed.
A better explanation happened in Superman vs Aliens. The battle took place on a planet circling a red star, and since Superman's might mostly comes from the radiation of a yellow star...
And when Superman fought Muhammad Ali, the aliens behind the Let's You and Him Fight had made sure it was under red star radiation.
Early in his superhero career, Spider-Man is actually beaten and unmasked by Doctor Octopus in front of his friends and family. However, Peter's powers were on the fritz at the time—he had lost his spider-sense and had his strength reduced to that of a normal teenager—and so no one believed that he was actually Spider-Man, but was just dressing up as Spidey in order to distract Doc Ock. Much later, when Peter revealed his secret identity to the world during the events of Civil War, Doc Ock went ballistic because he had known this information for years and never realized it was the truth.
A borderline case occurs with the death of Gwen Stacy, as Spider-Man was suffering from an unspecified illness at the time. This tends to be omitted in almost all retellings of the story, however; given that Gwen's neck snapped due to the abrupt stop from Spidey's webbing, it's questionable whether the illness was a factor at all in her death.
In the very first crossover between Superman and Spider-Man, Spidey initially holds his own because Lex Luthor and Doc Ock had unknowingly (to him) sprayed him with a blast of Red Sun Radiation. Superman is about to use a full powered punch when he realises that the impact would subject Spider-Man to the Chunky Salsa Rule and stops it short, the sheer blast of the punch knocking Spider-Man through several buildings (through their windows.) Spidey gets angry and charges Superman, only to have the Red Sun Radiation wear off just as he lands his first blow. As he puts it a couple of panels later:
Spiderman: Oboy. Oboy. I think I just broke my hands...
In the Spiritual Successor to this team-up, Batman vs. The Hulk, this trope is only enforced through Fridge Logic, as Batman 'wins' their first encounter through judicious use of his utility belt's knockout gas capsules. His ploy when the Hulk simply holds his breath is to kick him in the solar plexus, only working (as the narrative captions would have it) because the Hulk is so surprised at the fact of the blow rather then any physical pain and is forced to inhale the gas. Notably, when Batman tries this trick again, it fails, as the Hulk just waves the gas away with his hands.
Similarly, The Flash, when in the Marvel Universe during the JLA-Avengers crossover, was unable to run as fast as he usually does (and, eventually, loses his Superspeed altogether) because 616 lacks the Speed Force. Otherwise he'd probably knock every Avenger not named Thor unconscious about .5 seconds into the required "Crossover Fight".
In Knightfall, Batman begins with an unspecified illness and the plotline is based around how he completely wears himself out by trying to capture all the inmates the Dangerously Genre Savvy Bane has released from Arkham, positioning himself for the Curb-Stomp Battle Bats will eventually receive.
At least one earlier issue has brought up that Bruce hasn't truly recovered from what happened in Batman: The Cult.
The books show that it was a number of problems that had built up over time: his inability to capture Black Mask, beating beaten half to death by the spike-wielding Metalhead, his headbutting argument with Sarah Essen-Gordon, The Death of Superman - essentially a superhero Mid Life Crisis. Bane just picked the right time to run Batsy ragged.
Doctor Strange lost to Hulk during World War Hulk because he was channeling the powers of a demon that was too powerful for him to properly control, and because the Hulk tricked him and broke his hands to prevent him from properly casting spells.
When Doctor Strange helped found the original Defenders, his immune system apparently took a vacation. The writers admitted to brainstorming "how do we keep Doc from wrapping up the plot in one frame" almost every issue. Lampshaded when Doc took a break from the Defenders to figure out why he was having so much trouble with his spells.
Similar to the eternal Doombot excuse, Prometheus explained his embarrassing performances since his first, when he took on the entire Justice League, by explaining that in the intervening time someone had stolen his gear and impersonated him.
Retroactively done to every single Superman vs. The Flash race. Superman tries to convince Barry Allen not to return to the speed force and states that he's been able to keep up if not win in all their races. Barry simply tells him, "Those were for charity, Clark." Fastest man alive indeed.
The above was an odd case of this. Superman really was about as fast as Barry back when those issues were actually written, but Superman was powered down substantially in 1986 and, even if a lot of that power has returned he is not back to Silver Age power levels, so when those Silver Age stories became canon again, this explanation became necessary.
Thor is said to only use about a fifth of his full strength when fighting humans, even insanely strong ones like the Hulk, out of fear of accidentally killing them. One of the few exceptions (he specifically noted he wasn't holding back) was when he fought Iron Man after Civil War, and even after Iron Man's numerous upgrades in the past few years Tony didn't last thirty seconds.
When Supergirl first returned in 2004, she was shown outperforming Superman to the point where it was speculated that she might actually be more powerful. It turned out, this was meant to show that Superman had been holding himself back all these years out of fear of causing death or destruction (which Supergirl in fact does in the early issues because she doesn't know her own strength.)
So when the yellow-clad Weapons Master does fight the flu-ish Superman, this ironically makes Big Blue that much more dangerous. As he tries to explain to the bad people, he doesn't know if he can stop his punches from taking off heads.
In one Bronze Age story, Superman starts having Does Not Know His Own Strength moments, and fears his powers are growing beyond his ability to control. In fact, the reverse is true: the Parasite is slowly draining his powers, but he made a point of first draining Supey's sense of self-control that normally keeps them in check. Since he was no longer pulling his punches, they seemed more powerful even though his baseline strength was actually dropping. By the time he figured it out, the Parasite had already drained a good chunk of his energy.
Preacher; the flashback history of the hero's dad. All sorts of horrific things end up happening to Daddy simply because his army buddy was too damned stupid to go get the flu treated.
An issue of New Avengers had Wrecker narrating a fight between the titular team and The Hood's crime syndicate, explaining that he wouldn't have lost to Luke Cage, who is significantly weaker, if Doctor Strange hadn't confused him with his magic.
Hulk was on the receiving end of a Curb-Stomp Battle at the hands of Zeus. That wasn't because of this; rather, that battle was the flu to set up for the next story arch, which required the Hulk to be significantly weaker than his powerlevel at the time normally allowed.
In WolverineOrigins, Dog only attacks James (the future Wolverine) after James exhausted himself cage-fighting during the previous night. Dog had also slipped one of James' opponents a set of brass knuckles to make sure James would be injured even worse. And James still nearly kills Dog after Dog makes him remember that Dog was the one who fired the shot that killed James' father.
Rachel Grey aka Marvel Girl of the X-Men was the host of the Phoenix Force for a long while. Her relatively weaker power compared to her mother's stint as the Phoenix's host was due to Rachel actively suppressing the Phoenix's power. She mentioned at one point that she only allowed the Phoenix to use at most one percent of its power.
Doomsday has had this trope most every time after his first appearance. His first had him take out the ENTIRE Justice League of the time singlehandedly and fight Superman to a standstill to the death of both of them. Afterwards, his flu is that he gains intelligence and as a result becomes so scared shitless of dying again that he becomes unable to fight with reckless abandon and even later learns compassion, both resulting in Doomsday becoming much weaker and getting beaten by opponents that otherwise wouldn't be able to scratch him.
A sort of double example for The Spectre. His level of power means that any time he gets involved in a big event, he could kill the villain instantly. Given that this would make for dull stories, he tends to lose encounters with big villains. The writers do usually give some sort of in-universe reason for it. In Blackest Night he couldn't smite Nekron, because he didn't have a soul at all.
Red Sonja lost a fight to Dark Annisia, then Annisia revealed Sonja had caught a deadly plague. It is later revealed that it is not a plague at all, but a poison, and Sonja had been fed some during the party the night before the fight.
Averted in Avengers Arena. In response to the massive outcry over X-23 grabbing the Idiot Ball by attacking Apex (who was controlling a freakingSentinel) head-on and predictably getting Curb-Stomped, despite her focus issue playing up her Awesomeness by Analysis, Dennis Hopeless attempted to invoke this trope in the letters column of the very next issue by claiming Laura had to act fast and didn't have time for a better strategy. The readers, however, weren't fooled, and it just made Laura come across as an even bigger idiot.
In Star Trek II: The Wrath of Khan, the rather puny-looking Reliant sneak attacks the Enterprise and leaves the ship hobbling along for the rest of the movie, thus prolonging a confrontation that, under normal circumstances, would've resulted in the Enterprise mopping floors with the Reliant within about two minutes. Most of the crew being cadets didn't help, and Khan was Genre Savvy enough to have studied the Enterprise in detail.
This is also used to explain why a jury-rigged Enterprise in the following movie The Search for Spock is disabled by one hit from a "scout class" Bird-Of-Prey. Even the Klingon commander can't understand why he hasn't been blown to bits after his initial strike, saying the Enterprise outguns him ten to one.
Later, the far more advanced Enterprise-D almost gets blown out of space by an even clunkier Bird-Of-Prey in Star Trek: Generations, thanks to the Duras sisters getting their hands on their shield frequency (which apparently lets them fire through it).
In the same film, the Enterprise-B was so new most of its equipment wouldn't be in until Tuesday, and was only being taken out for a spin for the sake of the news crews. Also, it turns out that Earth, the main planet of the Federation, had no other available ships, leaving the Enterprise as the only one in the sector, because... uh, because... um...
In Hellbound: Hellraiser II, many fans were disappointed to see Series villain Pinhead and his cronies taken out by the new Cenobite, Dr. Channard. Many have written off his easy defeat due to him being weakened and disoriented by learning he was once human, a notion supported by Hellbound screenwriter Peter Atkins.
The Iron Man films do this. The first has Tony's ARC reactor stolen by Obadiah Stane, forcing him to use his original, which doesn't have the output to support the Mk. III armor. The sequel shows that the Mk. VI has high powered lasers that are only good for one use, which Tony uses to slice up some drones before Whiplash shows up. In the third film, Mks. 1-7 are destroyed, he's unable to access Mks. 8-41, and Mk. 42 is a prototype that hasn't been fully tested yet.
Predators: This happens when the "Classic" Predator similar to the ones from the old films faces the lead "Berserker" Predator from this movie. The Classic Predator has been tied up for a while and has poorly maintained equipment allowing for leeway when the new predator wins the fight, but even with this, he still puts up a hell of a fight.
The drone on Tower 49 in Oblivion (2013). It's being repaired and doesn't have any armor plating, so despite drones being tough as nails, it gets shot down rather easily.
In the fourth Riverworld novel The Magic Labyrinth, master swordsmen Cyrano de Bergerac and Sir Richard Burton take time out of a running battle to fight a (rematch) duel. Both are itching to see who's better, but they're both weary from battle, both slightly wounded, and have both been drinking to boot, and they're on a rapidly sinking ship (they really wanted this rematch). In the end, Burton draws first blood, and offers to help Cyrano to his feet... only for Cyrano to be shot by one of Burton's companions, who had no idea the duel was a gentlemanly one. Burton later (and during the fight too) wonders what the fight would have been like had they both been at their peak condition.
In Brisingr]], Paolini has made certain that Eragon has not had time to recuperate to his full strength since achieving his super-human power.
At the end of Eldest, Murtagh defeats Eragon while the latter is exhausted from battle. When this pair fought a second time Eragon was fully rested, at full power, and had thirteen elves assisting him, but still only managed to drive Murtagh off thus implying that the loser's exhaustion from the first battle was a non-factor.
In Men at Arms Lance-Constable Cuddy brags in one scene about his axe-throwing prowess; he's so good that he won the last contest he was in by a landslide, aiming at a target behind him, while he was sick with a bilious attack. Right now he's healthy as a horse. So don't mess with him.
In Going Postal Reacher Gilt hires Mr Gryle, a male banshee hitman, to kill Moist. Mr Gryle's supernatural fighting skill and awesome killing physique are talked up hugely, so why are Moist and Stanley able to beat him? Simple. Mr Gryle made the mistake of snacking on an Ankh-Morpork pidgeon before the fight, which gave him food poisoning.
In The Darkest Hour, Tigerstar sends Blackfoot to kill Stonefur, who he has in captivity. Blackfoot defeats Stonefur, but only because Tigerstar had been starving him for several days, and because Stonefur was tired from fighting Darkstripe just minutes earlier.
In The Lost Warrior, Graystripe is defeated easily by a kittypet named Duke. However, Duke defeated Graystripe so easily because he had been captured by humans and stuck inside a house for two months, leaving him out of practice.
In the Nightside series, the major players aren't instantly overwhelmed during the Angel War because the angels are weakened by the very nature of the place. The first time John and his allies successfully beat down the Harrowing, it's because his Enemies' homunculi are weakened from having to break through the wards that protect Strangefellows, some of which were laid upon the bar by Merlin himself.
Kindling Ashes: Corran losses his second bout in a tournament because his father demanded that he use his non-dominant hand. His reasoning was a "true warrior is equally skilled with both". When he gets into a real fight with raiders later in the story, he kills several of them without injury.
Episode six of Dollhouse features this canonically on both sides: when Ballard and Echo fight, on the surface it seems like it might be an even match that could go either way. Echo with her programming is probably the better technical fighter, but Ballard is very big, built like a brick house, and so tough he can take out four gun-wielding thugs with a plank after he's been shot—plus, he's a trained fighter, so all of his experience is real. However, he had been shot mere days ago, and was not looking to actually hurt Echo, as she's his best link to the case. Cue him fighting defensively and eventually getting worn down. On the flip side, Echo was also fighting in order to frame Ballard for shooting a cop, not to actually win, so while she wasn't fighting to win either, her goals were served by simply getting him to the right place at the right time and disappearing.
Spike's attempted rape of Buffy in "Seeing Red" only got as far as it did because a run-of-the-mill vampire had got a lucky shot in earlier (as she was staking him, no less). Both injuries carry over into Buffy's fight with a superpowered Warren - even with super-strength and near-invulnerability, he can tell she's off her game.
The eponymous star of Angel has a long history of losing fights with Slayers. Then, in the episode "Release", he managed a narrow victory over Faith (after a wonderfully brutal fight). Not only was Faith still recovering from a severe beating the previous day at the hands of an indestructible demon, the very next episode it was revealed that at the start of her fight with Angel she had pumped herself full of magic heroin.
In another instance, Hamilton stomping over Illyria happened only after she had been massively depowered, and it's probably telling that Hamilton didn't go anywhere near her until this had happened, and in fact when Wesley was studying her gave him a hint that led him to discover how to drain her powers. He even goes into an exaggerated Smug Snake routine to Illyria's face as he ponders why she can't beat him to a pulp.
An inversion takes place in Mahou Sentai Magiranger, where the Heavenly Saint Lunagel is defeated in battle by Wolzard partly because she went on her own, but mostly because he'd spent the past four episodes doing nothing but powering up.
Buddy Rogers' explanation – at least on television – for why he was crushed in his WWWF-title loss to Bruno Sammartino, in less than 48 seconds. Indeed, he supposedly had a legitimate heart attack not long before the match, but because few people – other than Sammartino who were associated with the match are still alive (much less in good health; Rogers himself died in 1992) and because Kayfabe was strictly maintained, theres' no way to know whether Rogers agreed to drop the title to allow his health to recover or if he was faking for some reason.
Just prior to the 1992 Royal Rumble, Intercontinental champion Bret Hart literally had the flu (or at least was booked as having one; nobody's really sure), one ranging near the 104 degree range. He lost the belt the night before the event to The Mountie, who then set the record for the shortest IC title reign ever when he lost it to Roddy Piper one day later at the Rumble itself.
Masakatsu Funaki was well known to be a great fighter, but he had a knee injury prior to his fight with Rickison Grace, which his younger opponent was not afraid to exploit.
After coming to WWE, The Big Show was rather horribly misused, ending up as a lower midcarder holding the Hardcore Title. About this time, Brock Lesnar had pretty much obliterated his way to the World Title. Deciding to make Show the next challenger for the belt, WWE bookers just cooked something or other up about "don't wake the sleeping giant", basically saying that the reason Show had been so low on the cards was that he hadn't been trying very hard to do otherwise.
May have been a Real Life dig at Paul Wight, who had been "fat-camped" down to farm territory OVW in the past for perceived shortfalls in dedication (and diet).
Macaela Mercedes had a less than decisive victory over Phoenix for the Glory Championship in The Apocalypse Wrestling Association, as she hadn't gotten over being sick(she avoided being pinned, did not submit and was awarded the title by decision after the match became a stalemate). This later lead a healthy Macaela Mercedes to become unusually aggressive in an effort to prove she deserved the belt.
Her feud with Nikki Roxx and Rain in WSU and participation in New Horizon Pro Wrestling's Hardcore revival left Mercedes Martinez worse for wear. Before these events she had managed to fight off both Jessicka Havok and Hailey Hatred in National Wrestling Superstars. After these took place she could barely fight Hailey Hatred one on one at an American Championship Entertainment show.
Used as an excuse so many times, especially when it's a massive upset or a loss that is much more lopsided than anticipated. It may or may not involve home court/field/ice advantage and it frequently involves injury and/or fatigue.
When your [[insert favorite team in [[insert sport here]] here]] loses a game.
The New Zealand All Blacks were favourites going into 1995 Rugby World Cup. South Africa was the host nation, but they hadn't even participated in the previous two world cups due to The Apartheid Era. However, a few days before the two sides were due to meet at the final, All Blacks came down with a case of food poisoning. They decided against re-scheduling the final to keep it secret from the Springboks even though it got to a point where at least one player threw up on the sidelines, and they narrowly lost by a drop goal from the South Africans in extra time. There is a conspiracy theory involving a mysterious "Suzie" concerning this food poisoning, although most fans now believe the illness was unintentional.
A legend has Auburn University cadets greasing the rails before an opposing football team from Georgia Tech arrived, causing their train to slide past the station, and forcing the team to tire itself out walking back to the stadium.
Averted in Game 5 of the 1997 NBA Finals between the Chicago Bulls and Utah Jazz, to this day thought of as "The Flu Game". According to The Other Wiki, Michael Jordan woke up the day before the game nauseated and sweating profusely. He was diagnosed with food poisoning. He barely had the strength to get up out of bed, and the Bulls trainers told him there was no way he could play in Game 5. The Bulls would be at a distinct disadvantage without their leader, because the Jazz had just won two straight games to even the series, and whoever won Game 5 would be one win away from the championship. But he rose out of bed three hours before tip-off, determined to play. And after a listless first quarter in which the Jazz ran off to a 16-point lead, Michael led the team back to a 90-88 victory, finishing with 38 points, seven rebounds, five assists, three steals and a block. And then his teammate Scottie Pippen helped carry him off the court.
In Super Bowl XXXIX, Terrel Owens caught a pass from Donovan Mc Nabb and had an open-field run to the endzone. Unfortunately for the Eagles, Owens was still recovering from a leg injury, allowing a defender to tackle him from behind on what would have been an easy touchdown had he been healthy. The Eagles proceeded to fumble on the next play and lose to the Patriots by 3 points.
Nearly every losing sports team ever. It can't always be the referees' fault.
In college football, a famous recent example would Colt McCoy at his last Rose Bowl Game. The momentum of the entire game reversed suddenly - all because McCoy got tackled by a nearly 400-pound man early in the game, taking him out of the game. It wasn't even an especially brutul hit, but the physics somehow left his arm with no sensation whatsoever. He didn't feel any pain and his arm hadn't suffered serious injury, but he couldn't feel the football contacting his palm and fingers and thus couldn't make accurate throws. Truly a bizarre moment in sports as a QB had never before been knocked out of an entire Super Bowl or BCS Title game before, much less on such an unusual injury.
Two recent NBA examples: The Spurs in 2000 and the Celtics in 2009 were defending champions but late in the year lost their best player (Tim Duncan for the Spurs, Kevin Garnett for the Celtics) for the entire playoffs and suffered an early playoff exit to an otherwise inferior team.
Oddly enough, at least in the US, defeats are always blamed on this while victories are credited to divine intervention. The reverse is almost never the case.
In Chrono Trigger there is a sequence where your party has all of their money and equipment taken from them. Unless you have Ayla in your party, this sequence becomes a stealth mission. Strangely, you are unable to fight even if you have magic.
In Prototype, halfway through the game Alex is given a "cure" that zaps him of all of his powers besides his strength, speed, and shapeshifting. He gets better.
In Super Robot Wars Original Generation Gaiden, many people seems to come to term that Lamia Loveless was hit with this trope that she accidentally got hit by so many Distress Balls. She only got caught by the Bartolls on the first place because she was not in her mecha (the same goes to Kusuha, Arado, Seolla and Latooni), and later on, Juergen managed to 'kill' her because for the same reason, added by the fact that she was just recently and forcefully been plugged out from her cockpit that binds her. She doesn't really have much impact after being rescued, but should you bring her to battle against the Bartolls in Chapter 34, she will express disgust on the Bartolls and show them that in the right conditions, they are no match for her. Unfortunately, however, she could never do it on Juergen (nor that she has any special lines against him when they face off in Free Battle).
In Golden Sun, when the party faces Saturos on the roof of the Mercury Lighthouse, they are able to defeat him. However, it's revealed that because he's a Fire Adept, he's weakened by being on the Water-aligned lighthouse roof (strangely enough, although Water Adept Mia is able to recover her MP, Fire Adept Garet suffers no disadvantages). Saturos is stronger (and backed up by Menardi) when fought on the complementary Earth-aligned Venus Lighthouse.
Something similar happens to their successors in The Lost Age. When you fight Agatio and Karst at Jupiter Lighthouse, they're tired and worn down from their fight with Isaac's party, while Felix and co. are at full strength as they were healed by Alex shortly before the battle began. Karst even acknowledges this at one point, but later attempts to double-cross you and invoke You Have Outlived Your Usefulness anyway.
The first Yellow Squadron member shot down in Ace Combat 4, Yellow Four, is revealed to have sortied with poorly-maintained engines.
In Zero Gelb 2 mentions that his squad would often be sent from one mission to another without even any basic maintenance on their planes. The result is a slightly easier Ace fight.
Given the power levels of many Touhou characters this trope is used by many fans to explain the defeat of certain characters, since everyone in Gensokyo is battling under the Spellcard system, and if they weren't Holding Back the Phlebotinum, the fighting between magicians, time-stopper, ancient vampires, embodiments of death and afterlife, immortals, wielder of NUCLEAR POWER, and assortments of gods would have wiped Gensokyo off the map.
In Warriors Orochi, this is how the Orochi beats the Tokugawa. They arrive and launched their attack on Edo castle just in time when Honda Tadakatsu is away scouting the area. Considering Tadakatsu is often considered Samurai Warriors' Lu Bu, the battle might have a different outcome if he is ever present.
In Warriors Orochi 3, several warriors end up dying in the normal timeline due to being weakened in a previous fight. Thanks to Kaguya's time traveling abilities, the heroes can go back in time and provide needed help for said warrior so that they end up surviving in an alternate timeline and join the heroes.
In Mortal Kombat vs. DC Universe the effect that causes the two universes to merge also evens out the power levels of the characters. Or else Liu Kang fighting Superman hand-to-hand would just be silly.
Zeus pulls this on Kratos in God of War 2 by tricking him into using a magic sword to defeat a giant statue at the start of the game. However Kratos had to deplete all his energy in doing so making him easy pickings for Zeus to kill him. As the end of the game shows though, Kratos at full power is more then a match for Zeus.
The statue's outstretched hand slamming into Kratos while his back was turned didn't do him any favors either.
The trope is inverted in Mass Effect 3, as Kai Leng is introduced in the midst of his attempts to assassinate the Citadel Council. If earlier gameplay requirements have been met, Shepard is able to thwart him with the help of Thane Krios, who was also an assassin but is now in the terminal stages of a fatal disease. As Thane puts it, "he let a terminally ill drell stop him from completing his mark."
In Fire Emblem: Path of Radiance, Greil's death at the Black Knight's hand is revealed to have been because of a number of factors. His weapon really was not a proper weapon to fight him, and Greil crippled his good arm because of a insanity-induced rampage he went on. When the Black Knight learns of this he realizes his victory was hollow.
In Borderlands 2, despite being built up as The Dreaded (as well as a playable character in a spinoff), Wilhelm goes down very easily when you finally fight him, because Handsome Jack poisoned him before the battle as part of a Batman Gambit requiring the Vault Hunters to defeat him as well as having agreed to throw the fight.
Used pretty often in World of Warcraft to justify "a small group of unnamed adventurers killed one of the most powerful beings on the planet with no help whatsoever from the Big Good's."
From Classic we have Ragnaros the Firelord, who was newly summoned from his elemental plane and C'Thun, an Old God who was at a fraction of his true power due to being sealed away by the Titans. Ragnaros was averted in Cataclysm, three expansions later, when players defeated him at his full power.
Burning Crusade gives us Kil'jaeden, the de facto leader of the Burning Legion, who was in the middle of a summoning and at about half his power - and players still needed help from a Big Good or two to beat him.
In Wrath of the Lich King, another Old God named Yogg-Saron is in the same situation as C'Thun.
In Call of Juarez: Gunslinger, Silas Greaves admits the only way he was able to survive a duel with John Wesley Hardin (one of the fastest gunfighters who ever lived) was because the latter was drunk after a wild birthday celebration and thus didn't count his shots.
In Kingdom Hearts I, Sora's party manages to rescue Hercules from Cerberus. As the party leaves, Phil is utterly flabbergasted as to how they managed to do it. Hercules then says that he had managed to "soften up" Cerberus a bit before Sora appeared. Later in the game, you can fight Cerberus at his full power.
In Kingdom Hearts II, Hercules has been fighting Hades' minions non-stop for days or weeks. When he fights Auron, he's so worn down that Auron is able to overpower him and would have killed him if Sora and friends hadn't saved him.
Archer is possibly the most powerful character in Fate/stay night, but he is handicapped somehow in almost every fight he takes part in.
Unlimited Blade Works route: Archer spends most of his time trying to manipulate events rather than fighting (on the two occasions he does fight, his enemy runs away after one attack). After this, he is cut off from his source of mana and his power fades until he's only keeping his body together through sheer willpower.
Heaven's Feel route: Archer is wounded by Saber as in the Fate route, then is forced to fight in poor conditions and exposed to attacks which ignore his usual defences.
The true most powerful character is the other Archer, Gilgamesh, who is stronger than all Servants combined. Why does he lose in all routes? He never fights with full strength. Why? Because of his massive ego. In Unlimited Blade Works, he doesn't wear even his armor in the Final Battle.
Lancer gets this too in the Fate route. His only accomplishments were fighting Archer to a standstill and attempting an instant-kill attack on Saber which failed...until you realise that this was before Archer was injured, Lancer was ordered to scout his enemies rather than defeat them, and it took the most powerful Servant in the story to kill him. He is notably more Bad Ass in the Unlimited Blade Works route.
Then there's Rider having a limited mana supply and not wanting to obey her Master's commands until the Heaven's Feel route, and Gilgamesh refusing to wear his armour against someone he viewed as an inferior opponent... really, this could be applied to most characters in the game at some point.
In all routes, Saber starts out being improperly summoned by someone who can barely use magic, so she has an incomplete connection to his mana and therefore has to recharge herself very often with large amounts of sleep and food, even if she uses only a little bit of her power. This is exacerbated by the fact that she took a cursed, slow-healing stab close to the heart soon after being summoned. It also doesn't help that, due to worries that Shirou's lack of mage skill would leave him open to mind magics, she doesn't let him know her true identity and holds off on using her Noble Phantasm even more than any other Servant. And of course, her Master being unwilling to risk her life if he can avoid it and being unwilling to fight as ruthlessly as possible is a pretty hefty handicap for a Servant of the Grail War as well, even though she herself isn't really all that much more ruthless than he is (especially compared to all the non Rin and Good Sakura Masters). The other Servants aren't pushovers by any stretch of the word, but as the two times she got a competent mage as a master showed, there is a REASON she's considered the strongest class.
TheFate/stay night Worf character, Berserker, has this arguably crippling him in UBW and definitely doing so in HF. In UBW, he's hampered in his fight against Gilgamesh because he's shielding Ilya as well (which is given a Shout-Out in one of his Fate/Unlimited Codes missions, where he has to fight his opponent while keeping the defenseless Ilya alive). In HF, he gets hit by a gamebreaker ability he can't actually fight against and is turned into Dark Berserker before he can truly fight. While in Dark Berserker form, the fact that he is killed nine times by the same attack is likely because all his stats had degraded...including Noble Phantasm, meaning God Hand no longer provided as good protection. And while the Berserker class amps his already legendary strength and speed, it leaves him unable to use any of his skills or non-auto Noble Phantasms, instead fighting almost purely on instinct, reflex and power. Which is enough to make almost everyone who encounters him wet themselves in terror.
Arcuied is operating far below her normal power in Tsukihime, as she is still recovering from Shiki slicing her into pieces, and has to devote almost all her strength to suppressing her bloodlust. This is probably a good thing for the sake of the plot, though, as with access to her full abilities, she has Story Breaker Power and would curb stomp everyone in about ten seconds flat. And in Ciel's route, where she does gain back some of her power, it's not a good thing.
In The Order of the Stick, Knight Templar Miko singlehandedly defeats the Order of the Stick to drag them in chains to Azure City. Later, after Miko kills Lord Shojo, Roy knocks her flat fairly easily, and mentions that this time, besides Miko having Fallen, Roy was using his Ancestral Weapon (which had been upgraded immensely) and not a stupid club. Also, Word of God says that the reason her clothing turned grey was because many of her magic items only worked on Paladins in good standing, which she was not at the time.
Durkon rationalises that the rain that prohibited the team from working effectively the first time they battled Miko was a divine sign that they weren't going to win this one. However, she did beat them a second time without the rain slowing the party down. Or he could've been trying to justify why he surrendered the first time and only healed the second time.
A version of this occurs in "Have Yourself a Monkey Little Christmas" in the Whateley Universe. Chaka is put in significant danger during a fight because she'd just had her hips broken and reset! This is also a Chekhov's Gun, as the need was stated around her first appearance! She does in fact win the fight, thanks to Chou's healing abilities.
Yet again, Fey's infamous fight against Mule is revealed to include a good bit of Flu. Fey fought her in an arena where she couldn't draw upon her powers. In fact, she was put in there specifically because the administration heard her say "But I can't do a fight in there! The Ley Lines are so tangled that I'll hardly be able to do anything!" Furthermore, her foe can absorb her magical abilities. What follows is a rather fun run-and-gun.
In the second-to-last episode of Red vs. Blue: Revelation, it's revealed that Tex is destined to always fail at the last moment, because she's based on the memory of the Director's lost love who died in combat, and the trauma of her death is an integral part of how the Director remembers her. This explains how, throughout the series, Tex always managed to get captured, killed, or knocked-out at a critical moment despite being the strongest character in the series.
Word of God has this as something that came into play during the formation of the Book One finale: giving Zuko injuries from both his ship exploding, and hypothermia from his near drowning experience in icy water, plus powering up Katara with a full moon that increases the power of her water-bending. Consequently, Katara managed to win her fight with him despite his much greater experience, and incapacitated him. However, when the sun rose, Zuko one-hit-KO'd Katara. During the third round, it was night again, they were in a freakin' snow storm (plenty of water to bend) and Zuko was half-frozen to death. The next time Zuko and Katara had a real fight he more than held his own against her.
Zuko is similarly handicapped by being unable to use any of his Firebending in his fight-to-a-draw against Jet in Book Two. Doing so would have exposed his identity, which, after an earlier incident in the season where he'd shown his firebending in a fight to defend a town and was then immediately thrown out of said town, caused him to hold back with Jet.
This applies in the Grand Finale. Although Zuko had gained insights into Firebending long lost to his people and was more emotionally centered than he had been in his life, Azula is still better than him in a fight, but she's had a Villainous Breakdown. Just before going into battle against her he mentions that he doesn't need Katara's help anymore because Azula is slipping and thus he can take her on his own, which he wouldn't be able to do otherwise.
Team Avatar tries to use this trope to their advantage, by attacking the Fire Nation during an eclipse, (which temporarily prevents firebenders using their powers,) with the intention of beating Fire Lord Ozai while he's powerless. Their plan doesn't work, because the Fire Nation had forewarning about it and prepared accordingly, and Azula manages to be a formidable opponent even without her firebending. However, it plays a big part in Zuko's Calling the Old Man Out as he wouldn't stand a chance against Ozai in a firebending battle but is more than a match for him with his swords.
This applies to the main character of The Legend of Korra. In the first episode, she loses to the Metalbending Police (but since they were police, she held back and wasn't really trying). Later, she loses to some Equalist chi blockers. Korra had no idea they were chi blockers until after they defeated her, though, whereas they had trained to fight benders. Korra struggles inside the pro bending ring, but between being restricted to only waterbending and having limitations on how much she can bend at a time (it's complicated), that's to be expected, and she does still win quite often. In her first fight with Amon, Korra was badly outnumbered, and he got the drop on her anyway. When Tarlok defeats her, he uses a Story Breaker Power that, as far as Korra knows, is impossible for anyone to even have, and which nobody but Amon can counter at this point. When Amon takes her bending, he uses that same power. Luckily, Korra still manages to win quite a few fights when she isn't at a huge disadvantage.
Shows up again in Season 3, this time dealing with Lin Beifong; after a physically and emotionally draining acupuncture session, she picks a fight with her half-sister Suyin and barely manages to hold on.
In addition its been noted said fight took place in a room crowded with the very citizens Celestia was trying to protect, meaning in all likelihood, she may have been holding back so as not to harm them and may have beaten Chrysalis otherwise.
In "The Crystal Empire", Shining Armor has his horn cursed by Sombra and is unable to use magic, leaving Cadance to maintain the barrier spell on her own, which she becomes exhausted from.
In "Equestria Games", the Anti-Magic field set up to prevent cheating also prevents the unicorns from using their magic to stop the falling ice cloud.
In The Venture Bros., Dermot "claims" the only reason Dean beat him up in a Wimp Fight was because he was sick at the time. Did I mention throughout that entire episode Dermot "claimed" that his hands were registered as lethal weapons.
There are fan theories that state that the reason Superman was so weak in the first season of Justice League is because he was still recovering from the war with Apokolips.
The suggestion is often made that the French lost the battle at Waterloo only because Napoleon was ill with piles (or some other complaint). There's a Voltaire short story called Lord Chesterfield's Ears that's based on this sort of idea. In the same battle, Ney's ill-conceived attacks against prepared infantry positions and infamous failure to bring the spikes necessary to disable the British cannon batteries after capturing them (thus allowing the British to retake the cannons intact and resume fire with minimal delay) has been blamed on post-traumatic stress disorder from his leadership of the rearguard during the disastrous withdrawal from Russia.
The Battle of Borodino, the turning point toward a Russian repulsion of Napoleon's invasion, was lost (according to some historians) because "Napoleon had a cold." Leo Tolstoy says of this that that means "the adjutant who forgot to give Napoleon his waterproof boots [two days earlier] was the savior of Russia."
The Norwegian Constituent Assembly storyline ended with Sweden taking over Norway during the fall of 1814. The King Elect of Norway, Christian Frederick, had to lay down his executive power, to formally end the strife, and let the Norwegian parliament (and government) settle matters with Sweden. The Convention at Moss, written August 14 1814, has a "secret addition" stating that Christian should "find an excuse" for giving up sovereignty. Hence, this trope came into effect, and Worf Had the Flu all the way from the middle of August until he left quietly in October. Officially, he was sick, but although suffering from fits of depression, he invoked this trope.
During the 2012 US presidential election, President Obama seemed extremely tired during the first presidential debate between himself and his Republican opponent Mitt Romney, who many thought dominated the debate. Al Gore suggested that it was because of the altitude of Denver, the debate venue.