In fictionland, anyone caught unaware may be easily, instantaneously and noiselessly incapacitated with a single blow to the head (or alternatively, a karate chop to the neck). A character thus treated will usually be perfectly fine afterwards; at worst they may have a headache, dizziness, slightly blurred vision, or in the very worst cases, Laser-Guided Amnesia. The real danger to their health is not the aftereffects of head trauma, but the Bad Guys standing around the operating table (or other heavy piece of furniture) to which they've been tied down. In other words, being clobbered on the skull has no real lasting effects which could hinder our protagonists for the rest of the plot. (This is why In the Back does not apply — hitting someone from behind is not really dangerous.)
Needless to say this is not Truth in Television at all; any head injury sufficient to cause unconsciousness may also lead to concussion, brain damage, or death, and at the very least requires prompt medical attention. In fact, even momentary unconsciousness is an indication that a concussion has occurred.
But in fiction, particularly in action genres, being knocked out is treated as nothing worse than a particularly hard nap. Heroes wantonly deliver painful and dangerous concussions to guardsmen, and friends knock each other out in disagreements, with little acknowledgement that brain cells are dying. In many role-playing games, knockout punches are actually treated as a form of nonlethal damage from which you recover quickly. Contemporary audiences are becoming increasingly canny about this, meaning the characters now typically use more elaborate, realistic, or permanent techniques for dealing with opponents.
A strong blow to head can also serve plot-related purposes - mostly mixing up thoughts and your perception of reality. The classic example is starting to believe your own cover story. This is not the case in Real Life.
The "karate chop to the neck" version may have been removed from modern TV because if you hit the right spot it actually can knock you out, though not without serious risk of death. It utilizes the Carotid Sinus Reflex (the reason you should not take a pulse at the neck) and is very dangerous. There have also been depictions in productions as varied as the lighthearted I Spy and as dark as Callan in which neck-chopping unambiguously is shown to be fatal because it breaks the target's neck.
Other variants of the trope:
In Western media, there's the punch to the jaw (AKA a "knockout punch"). Again, in reality this could inflict serious injury. In this case, not only to the victim, but the attacker (without hand protection) could very easily injure their hand; boxers and MMA fighters wear gloves not to protect their opponents' heads (which they don'tnote In fact, by making powerful blows to the head easier they may increase the risk of brain damage), but to protect their own hands (which they do).
Common in anime is the "sharp shot to the solar plexus", often used to subdue a struggling person. It makes it fairly easy to pick up the now-unconscious person and sling them over one's shoulder for easy carrying. Its effects are just as exaggerated as the Western version; in real life, such a blow does not cause unconsciousness but does cause the muscles of the diaphragm to spasm uncontrollably, making any activity requiring air very difficult. It is safer than a blow to the throat or the back of the head, but can occasionally lead to dangerous organ or nerve damage and is thus best avoided.
Choke Holds, where an arm around the neck is used to cut off blood to the brain ("blood strangle/choke") or oxygen to the lungs (chokehold, stranglehold). Properly applied, this is a safer and more reliable way of causing someone to become unconscious (even allowed in judo competition for many decades), but carries a risk of stroke or other dangerous problems if used on an older victim or one with a weakened circulatory system. It also tends to wear off quickly (as in, after a couple of seconds), or alternatively when it doesn't, cause varying levels of brain damage.
Another variant is instant knockout caused by shattering either a vase or lamp over someone's head or even just on their back.
The "karate chop to the neck" is still used constantly in shonen anime, but even with its credibility can have some ridiculous effects, particularly in Dragon Ball, where characters can shrug off blasts and blows powerful enough to pulverize mountains, planets, and solar systems, but one little tap on the back of the head and they're down for the count, usually coming to when it sits well with the plot, or rather whatever fight is going on.
Used rather absurdly in Hunter × Hunter, although with nods to its dangerousness. Killua uses it to quickly advance through a tournament, but says he has to hold back to avoid killing his opponents. Chrollo uses one faster than the human eye can perceive in order to make it look like a girl fainted next to him. Someone watching a frame by frame video recording of it notes that it's surprising that he didn't chop her head off.
In Inuyasha, the "sharp shot to the solar plexus" move was once used by Miroku to subdue a peasant girl whom he was trying to move to safety. However, the women of the village had also been possessed by a demon, which Miroku knew. Hitting them in that location was the only way to free them from the demonic possession.
Mazinger Z: Boss used the "low blow to the solar plexus" variant with Kouji to try to avoid he fought against the Mykene Warrior Monsters in the last episode. Maybe it was used in a more realistic way than usual, though, since when Kouji regained consciousness a while after, he seemed being in pain.
Panzer World Galient used the "karate chop to the neck" variant in episode 5. Hy struck Lord Protz in the side of the throat, and the blow was strong enough to slam Protz on a nearby railing.
Used inconsistently in the Ranma ½ manga and anime. Not counting the comedy Hammerspace hammers, or the ubiquitous Megaton Punch, there are many instances where these martial arts masters are knocked out with serious, deliberate blows to the head. Since these are people who have withstood the equivalent of exploding tank shells, mountains collapsing on top of them, and accumulative damage from prolonged duels, the ease with which they can be incapacitated with an elbow (or kick) to the skull is mind-boggling.
In Naruto, Sasuke knocks Sakura out with a blow to the back of the head before leaving Konoha. When she got up, it was exactly like she just fell asleep. To be fair, we don't know exactly how Sasuke knocked her out. We saw her face and heard a blow, and then she fell over.
Also from Naruto is the Waterfall Village OVA. Sakura is put in charge of guarding the children while Naruto and Sasuke are off doing other things. A little while later, cue karate chop to the back of Sakura's neck and her being knocked out. Her attacker then let's out a scoff, saying he can't believe she's actually a ninja if she got caught off guard that easilly.
Fushigi Yuugi plays it straight and parodies it. Tamahome seems to like striking people smack over the head, punching their jaws out, and taking out their guts. However, he gets a taste of this in the middle of the series from fellow Suzaku Seishi Nuriko.
Nuriko: (taps Tamahome on the back of the head) Tamakinsy-kins!
Tamahome: (gets his face smacked into his food)
Nuriko: (smiles innocently) That's funny! I just meant to give you a little tap on the head!
Subverted in Le Chevalier d'Eon in the scene where Robin tries to Pistol Whip a guard unconscious. He only succeeds in hurting the guard, and has to resort to a more vigorous attack to bring him down.
On December 18, year unknown, Kyon and the SOS Brigade finish a meeting and walk down the stairs. Everybody's at the bottom, and Kyon starts coming down. Somebody gives him a Tap on the Head. He rolls down the stairs painfully and falls in a coma for 3 days. Turns out in an alternate universe (don't ask), Kyon got stabbed in the abdomen and his friends from the original universe come and save him and to restore time and... You know what, it'll all make sense in Vanishment.
Played very seriously in Angel Beats!!: When Iwasawa was alive, her father smashed a bottle over her head when she was trying to stop one of his and her mother's fights. She was mostly alright until the next day, when she collapsed at work due to a cerebral contusion caused by the hit. When she woke up in the hospital, she couldn't use her voice, and died soon afterward.
In Elfen Lied, Nyu is a result of Lucy getting her helmet shot off by what looks to be an anti-materiel rifle, making that what constitutes as a tap on the head for a Diclonus.
In Princess Mononoke, Ashitaka uses the "stiff shot to the solar plexus" variant to knock out San and Lady Eboshi, thereby ending the fight between the two women.
Anime episode 33. Ichigo has just been healed by Hanataro after a fight with Renji Abarai. Ignoring Hanatoro's warning not to move or he'll re-open his wounds, Ichigo is walking away when he's suddenly punched in the face and knocked unconscious by Ganju Shiba so he'll have to rest.
Anime episode 43 has two examples. When a Soul Reaper is suspicious of Uryu and Orihime, another Soul Reaper knocks him out with a piece of wood to the back of the head. There's also a fairly ridiculous example where Orihime gets a chop to the neck by a guy that just wanted her to shut up. It's not played as okay on that occasion, as the man realises he hit her too hard and is very worried about what damage he may have done to her (none, as it turned out, meaning this trope was still played straight).
Hanaukyō Maid TaiLa Verite episode 2. While Ryuuka and Mariel are in a contest Ryuuka is hit on the head by a falling heavy metal basin and knocked unconscious. It turns out she was supposed to catch it.
In Gundam Wing Endless Waltz, there's a scene where Heero, Duo, and Trowa (the later posing as a member of the enemy forces) are cornered in a room. Heero asks Duo, completely out of left field, to punch him. Duo complies, and his right hook is "rewarded" with a shot to the solar plexus ("W-why?" "One for one; we're even now."). The idea was to knock Duo out so he could affect his own escape later, while Heero pretended to be KO'd and made a break for it when the soldiers were distracted by talking to Trowa, who pretended he captured the pair.
Sengoku Basara has Kojuro hit Masamune in the shoulder/neck area with the blunt edge of his sword, knocking him out. It causes no lasting damage but another character calls him out on the risk.
Homura does the "karate chop to the neck" trick to Sayaka in Puella Magi Madoka Magica. This one is especially weird, because Kyouko had recently smashed Sayaka against a wall, intending to cause serious injury, but her powerful healing magic kicked in and she got up immediately. Yet the karate chop causes long-lasting unconsciousness.
Played with, justified, and lampshaded in Cyborg 009. Joe is clubbed on the head by a giant monster. When he wakes up, he's very incoherent and in terrible pain as he gets back to his team. He needs a patch-up when he gets there, and 004 notes that the head injury he sustained would probably have killed a regular human.
In "The Further Adventures of Nick Danger", Nick gets hit on the head by Nancy/Betty Jo. As he slowly fades into unconsciousness, he begins to hear voices, one of which is the announcer saying, "we'll be back to Nick Danger after these commercial messages".
Astérix, Obélix and company frequently employ this against Roman legionaries, bandits, and other foes. Although "tap" is sort of a mild way of putting it, given their Super Strength.
In Astérix and the Big Fight, Obélix accidentally flattens Getafix the Druid with a menhir (causing the latter to develop temporary Identity Amnesia); he then describes it to others as "just a tap on the head".
It has to be noted that all injuries in this series are Amusing Injuries. The menhir example above is the one case where the injury had any long lasting effect.
The Belgian comic book character Tintin falls prey to this so often that one suspects he has a fainting button on his head.
In fact, in a joke section of a medical journal dealing with brain injuries it was once speculated that Tintin's perpetually youthful appearance was due to the repeated blows to the head damaging his pituitary gland and stunting his growth.
Action GirlYoko Tsuno, the main character of Roger Leloup's comic book of the same name, is an Aikido expert who uses the "chop to the neck" movement (which is named yokomen in Aikido) regularly on her rivals. Yoko herself frequently faints after being chopped on the neck, her enemies all seem aware of Yoko's vunerability in this area, almost as if Yoko has something on her neck that says hit me here to make me faint.
Happens to Hal Jordan almost constantly. Having a magic ring to help boost your biological systems helps.
The famous "One punch!" with which Batman knocks out Guy Gardner. The only after-effect is a comedy personality change.
To avoid the implication that Batman had given Gardner brain damage, the personality change isn't caused by the punch, but rather by Gardner bonking his head on the underside of a desk, after waking up from the punch.
That, and Gardner'd already suffered brain damage before. And was faking it here anyway.
Comic books RUN on this trope, especially the "punch to the jaw" version, which virtually every superhero uses as a standard method of dealing with mooks. One wonders if the general insanity of Gotham City criminals might be Batman's own fault, from dishing out so many concussions to formerly-ordinary thugs.
Inverted in the first issue of the Charlton Comics illustrated magazine version of The Six Million Dollar Man where Austin — depicted in the B&W title closer to the cold-blooded killer of the original novels than the TV version — karate chops a scientist in the neck with his bionic arm, obviously killing him, and then impersonates him for the rest of the story (after spending a night with his wife).
Graduate Meeting Of Mutual Killing averts this trope. The protagonist Akane Ogata gets hit by a piston, full force, and loses consciousness. While she doesn't die, when she wakes up she's drenched in blood and in great pain. Few moments later, she gets hit in the head again, this time falling into a coma.
Six Brides For Two Sisters has Rarity blocking Twilight from teleporting herself and other ponies away from an awkward social situation. When the guards come by, Twilight asks Applejack to do this (Twilight had mentioned earlier that if she were to just plow through the block, she might kill Rarity from the backlash), her waning sanity putting faith in this trope. Applejack disagrees. 'One, what Ah’m trying to say is that if I kick Rarity in the head hard enough to knock her out, Ah’m liable to cave her skull in, or break her neck, or somethin’.'
The My Little Pony: Friendship Is Magic fanfiction Jericho uses this in a very interesting way. It gets amazingly played straight, lampshaded, subverted, and deconstructed—all in one chapter! First Jericho knocks a stallion unconscious with a side-neck chop, has a What the Hell, Hero? moment on himself wherein he lampshades this; then when Jericho himself get a nightstick upside the head, he only gets a nasty, nasty bruise. (The deconstruction is the head injury he gets and how he could have killed that one guy.)
Jericho: “Oh, you mean the side-neck chop? That’s just a martial arts move. I mean, yeah, if I’d done it wrong, it would have killed him via cardiac arrest, and so, in hindsight, that was highly irresponsible of me to do but... I’m not helping my case any, am I?”
Summer Days And Evening Flames: Farrington Guard Captain Iron Bulwark is on the receiving end when Sergeant Sherry escapes his custody. He assures the two guards (actually one) that he's okay, and is sent all the way to the hospital to confirm that he's okay.
Narnia fanfiction The Fledgling Year does this consistently. Whenever a character is knocked unconscious by a blow to the head, they’re typically only out for a moment (the exception being when Aravis falls off a cliff in chapter 54), and usually don’t suffer any permanent damage. The common version of this trope, the “knockout punch” to the jaw, is subverted and then lampshaded by Cor:
Cor: “… I barely had time to put my hands up when one of them hit me in the jaw—I could tell they were only common thugs, since even I know not to punch the face. He fell back yelping about his knuckles …"
Subverted in the Chris Farley comedy Almost Heroes. Chris Farley's character Bartholomew Hunt attempts to hit his companion Leslie Edwards, played by Matthew Perry, with a rock in order to knock him unconscious (for Leslie's own good; It Makes Sense in Context), but only causes considerable pain. He then picks up a comically-large rock that would almost certainly crush Leslie's head in and is about to try again before Leslie stops him.
Also subverted earlier in the movie when a dentist, about to remove one of Bartholomew's teeth, hits him over the head with a hammer to knock him out. It doesn't work, and Bartholomew just tells him to get on with it.
A Water & Power trooper knocks out Tank Girl after capturing her outside her house.
Tank Girl knocks out Sub Girl (AKA "Rain Lady") by tapping her on the top of the head with a plastic fish.
A Water & Power guard is knocked out from behind with a bowling pin.
Subverted in Dog Soldiers when Wells (Sean Pertwee) orders Cooper (Kevin McKidd) to knock him out, so Cooper hits him, but Wells just sits up again and shouts, "I said knock me out, you fucking pussy!" Long term damage isn't an issue in this case, since Wells has been bitten by a werewolf...
While Austin and Vanessa are infiltrating Virtucon, Random Task comes up behind them and smashes their heads together like coconuts, rendering them unconscious.
Vanessa cracks Random Task over the head while he's in their suite. That hat certainly wasn't effective.
In The Boondock Saints II All Saints Day, this is subverted and parodied mercilessly. A part of the plan that Murphy and Conner comes up with to get rid of a small time drug ring calls for a friend of theirs to club a fork lift driver in the head to steal a forklift, and you can tell it's doomed to failure right away when they give him a gun that's so small it looks like it couldn't kill a bird. After a Gilligan Cut, we see the forklift driver they tried to KO with a nasty gash in his head, chastising them for the over reliance on tropes in their plans, asking why they just didn't wave a gun in his face and tell him to scram.
In the film version of Johnny Mnemonic, Ralfi is being held against the wall by Johnny. Johnny is then promptly cold-cocked in the back of the head by one of Ralfi's bodyguards, and collapses like a sack of potatoes. It is some consolation, however, that Ralfi is worried that it may have caused damage to his head because the Yakuza thugs want Johnny's head intact.
Subverted in The Gamers; one of the PCs asks to be knocked out. Two characters hit him, to no avail. The third knocks him very much out, so much that he's killed. Obviously, the rules of their game don't allow for non-lethal damage.
This has happened to James Bond (and others in his movies) repeatedly.
In Who Framed Roger Rabbit, Roger is bopped over the head with a frying pan and dragged out of the way. Later, Jessica reveals that she did it: she didn't want Roger to get hurt. In fairness, it's impossible to permanently injure a toon via this method.
Big Trouble in Little China. Wang and Eddie take out some female guards with judo chops and karate kicks to the head, and Wang knocks out multiple Wing Kong guards with punches and kicks to the head. Amusingly, Jack Burton knocks himself out by shooting the ceiling and dropping masonry on his head.
Mortimer: (watching the fight). "Oh, don't do that. It never works." (Jonathan collapses) "What do you know? it worked!"
In From Dusk Till Dawn, sick of Richie's psychotic behavior when the family whom they've held hostage's van hits a bump, Seth uses this opportunity to punch him out.
Star Trek: Generations. While in the Amargosa Observatory, Dr. Soren knocks out Geordi LaForge with a punch to the face.
This is not done once, but twice to Captain Jack Sparrow in Pirates of the Caribbean: The Curse of the Black Pearl - First, humiliatingly by Will Turner's drunken blacksmith and then by Turner himself while spying on his mutinous crew in Isla de Muerta after Will figures out that Jack wishes to use him as "leverage" to get his ship back.
During the Black Pearl's attack on Port Royal, Turner himself gets knocked out during his fight with the undead pirates and wakes up dazed the next morning.
Blazing Saddles. After Taggart leaves Bart to die in quicksand, little realizing that the quicksand in this movie, apart from being in the middle of an arid desert, works exactly the way it does in real life (i.e. it doesn't suck him in, among other things), Bart comes up behind him and lays him out with a shovel to the back of the head. Later on Taggart has a bandage on his head and not even a concussion.
Although Taggart does scream in pain when Hedley Lamarr touches the bandage, so obviously there was some injury done.
Both used and averted in the Ip Man films, where a good blow to the head drops many a mook, but named characters prove more resilient.
Flash Gordon. Voltan hits several of Ming's goon squad members over the head with his mace during the "football game", and Hans Zarkov knocks out Flash accidentally by throwing a hollow metal "football" at him.
Beverly Hills Cop. One of Maitland's mooks knocks out Axel Foley with a blow to the head before Mikey is killed.
In the second of these, there are two clearly audible blows after Dr. Jones hauls the guard over the pile of boxes, so it's "Taps".
Red Cliff - Shangxiang displays her excellent knowledge of pressure points by knocking out an uppity official's horse when he snarks about a woman being on the battlefield; later, when being introduced to Liu Bei, she expresses her unhappiness about being presented as a possible marriage prospect by doing the same on him. (Cue looks of Oh Crap on Zhuge Liang and Zhou Yu's faces as they realize what she's up to, but are too late to do anything...)
Constantine. Constantine knocks the bouncer in Papa Midnite's bar unconscious with one punch.
Subverted in High Risk (1981) when the heroes encounter a servant while sneaking into the drug lord's mansion. The servant just clutches his head and screams, alerting the guards.
Disney's Bedknobs and Broomsticks. Two of the German commandos are knocked unconscious by the animated suits of armor: one by a punch and one by a literal "boot to the head" - a swung iron boot, that is.
In Howard Hawkes' El Dorado, John Wayne is taken prisoner when the Dragon sneaks up behind Mississippi and "give me a headache."
Cowboys and Aliens. Jake is knocked out by getting pistol whipped on the back of the head and wakes up an unspecified amount of time later with no lasting damage.
Judge Dredd. When Dredd and Ferguson are in the Judges' locker room, Fergie distracts a Judge and Dredd knocks the Judge unconscious with one punch.
Subverted in Funny Farm. When one of the locals gets a fishing hook stuck on his face, Andy wants to knock him out so he can easily take out the hook. After several blows, the man is not knocked out, just pissed off, and one of his friends wonders if Andy is just beating him up.
After he enters Castle Brunwald, Indy knocks the butler unconscious with a punch to the face.
Averted when Indy's father tries to knock out Indy by breaking a vase over his head. Indy stays conscious and is annoyed with his dad.
During the fight inside the tank:
A German soldier is knocked out when a periscope handle hits him on the back of the head.
Another soldier is rendered unconscious when Marcus Brody hits him over the head with an object.
In Jean-Claude Van Damme film Cyborg, Van Damme's Faux Action Girl sidekick gets knocked out 3 or 4 times in the movie. Van Damme's character gets KO'd once or twice as well. No one seems to have any problems because of it.
In Lock, Stock & Two Smoking Barrels, Dog knocks out a traffic warden with one punch and stashes him in a van. When the main character steal the van, they discover the meter warden and try to knock him out again, but he just makes a pititful, "Owww!" After realizing that they all hate traffic wardens, they gang up and pummel the poor guy into unconsciousness.
Averted in the opening of Tamara, where the title character is killed when she knocks her head on the edge of a table. Played straight, though, when Chloe punches out Kisha and when Allison knocks out Sean; both of them later get back up from it.
Played straight when Kirk whacks Scotty over the head then straps him into a seat for good measure to make sure he can't stop him from climbing into the radioactive warp core chamber.
Spock does this to Harrison during their brawl, but it doesn't knock him out.
Mars Attacks!. After Jerry Ross allows a strange woman into the White House in order to seduce her, she bites off his finger and knocks him unconscious by hitting him on the back of the head with a statuette. She turns out to be a Martian assassin wearing a human disguise.
Occurs many times in The Rocketeer. Played with here in that the victims often recover faster than their assailants were planning.
In Danger: Diabolik, the morgue attendant gets this via an urn wielded by a disguised Diabolik as he scrapes Ralph Valmont's ashes out of the retort. He apparently leaves him lying there alive, because when, as he leaves the morgue with the eleven emeralds, an elderly couple asks if he's seen the doctor, he simply says, "He's in shock."
The Wizard of Oz: Dorothy is knocked flat by a fairly light bump on the head from a falling windowpane, and suffers no ill effects (though her family and friends have clearly been worried about her when she wakes up) except a fantasy-filled Technicolor dream sequence.
The 1974 film spin-off of Callan includes a sequence in which the hero kills a man with his bare hands. He first delivers a sharp blow to the solar plexus, then a second blow to the jaw or neck, but the killing blow is a karate chop to the neck, averting the non-lethal aspect of the trope.
In Thief of Time, it is mentioned that some trainees in the Thieves' Guild cause serious injuries with their inability to knock a victim unconscious with a single blow. Likewise in Monstrous Regiment, one character is about to knock a guard unconscious when The Igor points out that blows to the head can be fatal and takes over, as Igors have extensive knowledge of human anatomy. So extensive, in fact, the Igor knows just how hard and where to hit to knock the guy out for exactly 20 minutes.
Additionally in Men at Arms someone is accidentally killed by an attempt to knock them unconscious.
Not seen, but referenced in Night Watch, when it's mentioned the rebel barricades have a doorway built into them, with all refugees coming through at just the right height for "a gentle Tap on the Head if they turned out to be a soldier."
Vimes in particular plays this trope quite straight. But, like Igor, he knows exactly where and how to strike—at one point he stops his less-experienced younger self from delivering such a blow and does not teach other coppers how to do it right if they approach him privately.
In Interesting Times, a briefly deranged Rincewind is used in an impromptu demonstration when a Thief's Guild apprentice tries and fails to knock him out. So the tutor steps out of the nearby alley to show him the right way ("Ow."), then what the trainee did ("Ow! Hahaha!" "So, can anyone spot the difference?"). It isn't until he regains his senses that he succumbs.
In Maskerade, someone tries to knock out Nanny Ogg with a bottle. Nanny sees stars, but since she has a bit of dwarfish in her ancestry, she recovers without passing out, and chases the attacker.
In Stephen King's It, staff of the Juniper Hill mental institution use rolls of quarters as improvised saps in order to subdue (and, in some cases, simply abuse) recalcitrant patients. One patient is said to have suffered severe brain damage as a result of such treatment and is barely functional as a result.
In The Langoliers, government assassin states that he knows a many ways to kill a person, but doesn't know a single method to safely render someone temporary unconscious.
Mentioned in the novel First Lensman. A thug of wide experience claims to be "an artist with the black jack". His boast is that he can knock out anyone within ten feet by throwing it, and can precisely time how long they stay unconscious.
Subverted in John C. Wright's Fugitives of Chaos. Amelia is able to work out, from the fact that she is not suffering plausibly from a blow to the solar plexus, that magic is at work.
Earlier, she tries hitting someone with a rock to escape custody. It doesn't work because: a) she was too squeamish to hit hard, b) a rock is not going to stop a Physical God.
Burke gives a bit of a Character Filibuster once about how hitting someone on the head does not always knock them out in real life, and how many would-be criminals have gotten into trouble that way.
Averted in The Atrocity Archives by Charles Stross. The protagonist is hit on the back of the head with a sap (a bag full of lead shot) knocking him out. He spends a couple of weeks recovering, and got a hairline skull fracture for his trouble.
In Isaac Asimov's The Currents of Space a character attempts to pull this off on a guard and accidentally kills the guard.
In Alistair MacLean's novel Ice Station Zebra the doctor protagonist goes into detail about how it is impossible to predict the consequences of a head injury, i.e. the patient could wake up soon or never, then later on has someone else inflict a "ten minute tap" on a villain. However, the doctor also explains to that chap that his huge wrench would cause instant death when hitting a skull. The doctor pads the wrench with a thick layer of bandage to make it less lethal.
Richard Henry Benson, The Avenger is capable of doing this—with bullets! In "The Yellow Hoard" he is distracted by smoke sufficiently that he missed his target by a millimeter, and the thug wakes up too early.
Jame in P.C. Hodgell's Chronicles of the Kencyrath is knocked out by blows to the head all the time, both by accident and malice, and is always fine. It seems to happen at least twice per book. It's justified in that she's not exactly human, and her Healing Factor ensures she repairs; also, realistic effects of concussion appear when the blows were severe.
Lampshaded in the Doctor Who novel "Interference: Part 2", with Sarah Jane Smith asking an alien how they can manage to knock people out without long-term effects so easily. (Since the alien in question was not very bright, no answer was actually obtained).
In Broken, Elena needs to sneak away from her assigned babysitter. So she hits him on the back of the head, arranges him comfortably on the bed, and takes off. Justified in that he's a werewolf, and she really doesn't need to worry about long term damage. Subverted in that she didn't actually knock him out at all; once he realized what she was trying to do, he faked unconsciousness and then followed after her.
The main character of Dave Duncan'sThe Seventh Sword tries this on a guard in the first book. However, the person he hit ends up dying. It comes back to haunt him later, when he ends up on trial for various crimes, one of which is this "dishonorable" killing. (After some Divine Intervention makes it clear that the Goddess doesn't want the main character punished, the death is ruled an accident; after all, if he had wanted to kill the guard, he would have used his sword, not his fist.)
In the Forgotten Realms novel Ghostwalker a knight knocks out a drunken rogue in a bar fight using a mace. Not a club, a flanged metal mace.
Averted in Neuropath. Tom Bible notes that it's not like in the movies, and that the guard he and Mia knocked out will need medical help quickly.
The Vulcan Neck Pinch chapter of The Action Heros Handbook outlines several of the knockout methods mentioned above and makes clear what the risks are.
When they need to avoid their usual, lethal methods, the protagonists of The Belgariad employ this trope frequently to render bad guys unconscious. It's usually played completely straight, except where Hard Head is subverted by Rule of Funny or the needs of the plot.
On one memorable occasion, after Garion knocks out a Grolim (who has some useful information), Belgarath tells him to "use an axe or a club" the next time: Garion's fist had almost killed the guy.
Averted in the Sword of Truth series, when Kahlan is trying to decide the best way to make her way past a D'Haran guard. There is a long inner monologue about how a rap on the head is notoriously unreliable: the guard may come up screaming, several blows may be necessary to induce unconsciousness, and permanent damage may result. Additionally, this is one of her own guards, so she'd really rather avoid hitting him at all in the first place. Later on in the series, she shows a little girl she is held captive with her preferred way of silent subduing: A knife to the kidney. Where a blow to the head is unreliable and cutting the throat can be too messy and loud, a knife to the kidney puts the victim in so much pain that they can't even scream.
This is practically the Signature Move of Karl May'sAuthor Avatar Old Shatterhand/Kara ben Nemsi, ostensibly justified by a combination of nigh superhuman strength and a special trick he's discovered himself. It's rather convenient, too, because as a good (if sometimes, especially in the later works, a bit preachy) Christian the character doesn't actually like to shed human blood when he can at all avoid it.
Lampshaded in The Dresden Files when one of Harry's internal monolgues mentions that someone must have done one of those adamantium upgrades on his skull.
Also retroactively justified by the author, after it was pointed out to him that with all the blows Harry takes to the head, the concussions should have added up and left him brain damaged. So to justify this, and the Wizards Live Longer trope also prevalent in the series, he had a doctor give exposition explaining that Harry, and all wizards, have better healing ability than muggles. Any injury Harry takes will heal at a normal rate, but will heal completely, to the point where previously broken bones eventually show no scarring, and a burned hand that a doctor advised he simply amputate is back to fully functioning after a few years. It's even mentioned in Changes that Harry's broken spine might well heal on its own, given enough time.
Averted in Martin Caidin's Cyborg novels. Considerably violent than the TV series they inspired, due to Steve Austin's bionic arm being described as a bludgeon, and strong hits to the head or chops to the neck are instantly fatal to the recipient. In fact he does this so often (sometimes cold-bloodedly to disabled enemies) that fans of the TV series are prone to go into What the Hell, Hero? mode when reading them.
In Death at the President's Lodging by Michael Innes, the detective investigating the aforesaid mystery is knocked out by a blow to the head. One of the suspects, an author of detective novels, says that he'd never have done it, because he knows how dangerous such a blow could be.
In the Time Scout book, Wagers of Sin, Skeeter gets knocked out from behind and spends several days recovering, with nausea, dizziness, and continuing headaches.
Completely averted in Vernor Vinge's The Children Of The Sky. The blow that knocks out Ravna is treated completely realistically, with various debilitating aftereffects until she gets advanced medical treatment.
The Hardy Boys: Frank & Joe Hardy have both been knocked out by getting hit in the head so often that, in real life, the two should be vegetables in permanent coma in the hospital.
In Michael Flynn's The January Dancer, the Fudir uses this on Hugh to evade him. He does think that it's a tricky business, but it's treated as if it were really harmless.
In Seanan McGuire's Velveteen Vs the Junior Super Patriots, the Claw strikes down Velveteen with a head blow. Though it does only knock her down, rather than unconscious, so the lack of lasting harm is more plausible.
In Andre Norton's Catseye, Troy enforces the promise to for a Mercy Lead by using Rerne as a human shield, and puts him out with this when he reaches the vehicle.
The Mortal Instruments: Sebastian renders Isabelle unconscious in City of Glass with a hammer after he finishes with Max.
Averted in The Curse of Chalion. When Umegat is found unconscious by a blow to the skull everyone remotely familiar with head injuries treat it as a life-threatening emergency and when he awakens days later he is revealed to have suffered serious brain damage.
Averted in one of the Mr. Midshipman Hornblower stories. Hornblower strikes a man with the rudder because he's having a loud epileptic fit during a stealth expedition. Hornblower is pretty sure that he's killed him by doing this (although the boat is lost, so we never find out for sure). The TV adaptation uses this scene, but winds up playing it straight.
Nick Moss is knocked unconscious by the phantom biker Cacophony Jones near the end of City of Devils. This is after Nick has done similar to another member of Cacophony's band, the Disasters, so it's decent payback. Also, Imogen Verity knocks out the other two earlier in the book. It's a bad day for head trauma in the Disasters.
Averted with Mattes Tunstall in the Provost's Dog trilogy, who is described by Beka in the third book as having suffered so many taps on the head in the past that if he got one more, he could very well die of it.
The Elephant's Tale averts this. One of the staff is knocked unconscious during a burglary, and is incapacitated for the rest of the story while they take him to a doctor.
Live Action TV
LOST has used this a few times, though the preferred method of knocking someone unconscious is Pistol-Whipping.
In "Hearts and Minds," Locke hits Boone to knock him out, ties him up, and sends him on a Vision Quest by "treating" the wound with a hallucinogen.
More realistic effects of a Tap on the Head are shown in "The Other 48 Days," in which Eko kills two Others with a rock.
The series is actually quite guilty of this, as characters would be knocked out with a tap every other episode but only when it would fit the plot. All the fighting scenes feature much harder blows then those who render them unconscious. Almost every major character took a beating at some point with a lot of hits on the head but we rarely see one fainting.
In the episode "Last Stand", Mac is holding some piece of equipment that he's supposedly going to use to fix up a plane so the bad guys can escape. When asked by his guard what the item is, he replies "Lateral... cranial... impact... enhancer", and smacks the guard across the head with it.
This happens all the time in MacGyver, what with his no-guns policy. The likelihood of knocking a bad guy out with a single blow is inversely proportional to his position on the bad guy ladder.
Legendary subversion: in the first season Mr. Spock was scripted to incapacitate a maddened Kirk by rapping him in the back of the head with the butt of a phaser pistol. Leonard Nimoy thought that uncivilized, so he and the director came up with a more "civilized" alternative: the Vulcan nerve pinch (AKA neck pinch). Spock repeatedly used the nerve pinch in subsequent episodes. In one of them ("Mudd's Planet"), the pinch failed because he was using it on an android.
"Obsession". Ensign Garrovick tries to knock out Captain Kirk with a karate chop so he can be the one to lure the vampire cloud to the antimatter bomb.
Kirk himself was not adverse to a chop or hammerblow now and again. Even McCoy has been seen doing this occasionally...
A truer subversion is seen in the episode "Mirror, Mirror," in which mirror!Spock is knocked out this way and Dr. McCoy declares that he'll die without immediate treatment. It may have averted the trope too far, though, considering the deadly object was a skull so fragile that it completely shattered after hitting Spock. It's difficult to imagine it would even knock him out in the first place, unless the skull was so hard it took a lot of blunt force to break it.
Subverted in an episode of Red Dwarf. Kryten has to render the rest of the crew unconscious, but Rimmer is a "hard-light" hologram and thus "unknockoutable" despite Rimmer's assistance and Kryten's most enthusiastic efforts.
In Buffy the Vampire Slayer, Giles getting knocked unconscious occurs so often it's turned into something of a Running Gag. The jaw-punch version occurs in "Prophecy Girl", when Buffy settles the issue of who is going to fight the Master by punching Giles in the jaw, putting him to sleep just long enough for her to be off on the mission. Later Giles is seen nursing a bruise, but it seems no dental attention was required. The trope is subverted when Warren's ex-girlfriend Katrina is escaping the Trio's lair and plans to go to the police after their attempt to rape her. Warren clocks her on the head with a bottle, trying to knock her out — and she dies.
Played mostly straight in Angel, when Gunn has been turned misogynist by a demon. Realizing what's happening to him, he warns Fred to knock him out, but her first attempt fails. He yells at her for this, but it isn't really a subversion like the above example; Fred's not terribly strong. Her second attempt succeeds.
Played straight in Teen Wolf. Poor Stiles. The werewolves seem to consistently forget that whacking a human on the head can cause permanent brain damage.
Heroes uses it so much - for both comic and dramatic effect - that the show's Wiki has a page dedicated to it. Once, Claude saved New York (at least for the moment) with this trope and a good right hook.
Subverted in one episode when McGee sees a witness to a murder get attacked from across the street. He heads over to her apartment, only to find her door open. While he's seeing if she's alive, the assailant pops out of one of the rooms-which McGee didn't check-and smacks him over the head with a lamp. Despite getting hit hard enough for the lamp to break, McGee is still clear enough to unholster his gun and take a few shots at the fleeing perp, missing by inches.
Another painful subversion was when it was determined a man confessing to the murder of his fellow marine had actually Pistol Whipped him so he'd stop screaming after being wounded on a battlefield. The blow had cracked the skull and killed the man, his best friend, and the guilt had eaten at him for years.
In Buck Rogers in the 25th Century, Buck could take out a whole swarm of Draconian guards with a single sidekick. They fell like a stack of dominoes.
Get Smart, being at its core a Bond parody, did this constantly. While Max was an accomplished martial artist, his preferred method of attack was a karate chop to the back of the neck, either by waiting for somebody to enter the room, distracting them, or sneaking up on them. At one point, he ambushes five KAOS agents in a row as they enter a room. Unfortunately, the sixth person is a CONTROL operative.
The Third Doctor used "Venusian Aikido" to immobilise someone, which seemed to involve John Pertwee jabbing two fingers into someone's chest and shouting "Hai!"
This is a preferred technique of classic Doctor Who baddies; a nondescript karate chop to the shoulder which had a 50/50 chance of knocking people out or killing them outright.
In "Full Circle", the Doctor himself gets this treatment — keeping him from calming the alien child.
In "The Masque of Mandragora", when the Doctor realizes that Sarah Jane is being kidnapped and tries to intervene, one takes him out with a rock to his head.
Played with in the Tenth Doctor episode "The Idiot's Lantern". The Doctor is knocked unconscious by a punch to the jaw, but he only remains so for a few seconds and quickly gets back up in pursuit of the people who punched him.
An episode of Smallville has Clark knock someone out with a literal tap on the head. You get one guess why.
The Karate Chop of Doom was the standard fighting style, aside from fighting dirty. It can be considered acceptable, as most of the time they're trying to kill each other anyway.
Interestingly enough, Avon once tried to subdue a maddened Blake using this technique, which was rather risky. Then again, his relationship with Blake being what it was, it may have been intentional.
Averted once in the fourth season, when a genius robotics expert Avon wass hoping to recruit for something had some kind of manic episode and attacked Tarrant and Vila while en route to Xenon. Vila was forced to wallop him with a wrench in self-defence, and then all hell broke loose because it appeared he'd inadvertently killed the guy. Then things got weird...
Averted in season one of True Blood; Lettie Mae hits Tara over the head with an empty Jack Daniels bottle, which hurts a lot, but doesn't knock Tara out.
The MythBusters dabbled with this trope when they tested whether an empty beer bottle was more lethal than an full beer bottle. Either way, the least you would get out of a full strength blow from either bottle would be a nasty concussion, as well as lacerations from the broken glass. In the case of a full beer bottle, if your skull isn't completely caved in, then you're likely to suffer a catastrophic cerebral hemmorhage.
Similarly tested on Deadliest Warrior with a pistol whip. If not fatal, it would be catastrophic and permanent injury.
Subversion: In one first-season Sledge Hammer!! episode, Sledge jumps a Mook from behind, and hits him over the head with the butt of his gun. The Mook's reaction is to cry "Owww," but not to go down. Sledge tries again, with similar results. After several attempts, he is unable to knock the mook out by hitting him on the head. Alan Spencer, creator of Sledge Hammer!!, in his voice-over commentary for the episode, states that this was the entire purpose of the scene — to take the Mickey out of this trope.
In Leverage, the trope gets played extremely straight with Elliot and his one-shot knockout punches. Whether it's in the middle of melee or cold-cocking someone, one shot typically knocks them flat on their back and dreaming with no shown side effects afterwards. He's even used it on occasion on people entirely unaffiliated with the crime, simply to get their identification.
In Firefly, Mal delivers one to Jayne with a wrench.
He's only out for a couple seconds, though; and "unconscious" wasn't the specific intent, just a bonus.
Data has a convenient on/off switch under his shoulderblade.
Picard has been known to dole out a few back-of-the-head hits...but he tends to receive them more than he gives them.
A Running Gag in Dans une galaxie près de chez vous involved people doing this to Brad (saying "no Brad!" in an increasingly bored tone) at least once an episode to stop his "evil" plots to ruin the mission. He even does it to himself a couple of times.
On Republic Of Doyle Jake gets hit on the head so much every epeisode that he should be dead or suffering massive brain damage. In one episode he got hit in the back of the head by a crowbar and later by a wine bottle.
Averted in the original I Spy television series. In one episode Alexander Scott (Bill Cosby) attacks a guard with several karate chops to the neck and goes out of his way to explain to the person he'd just rescued that the guard was now dead. This is a rare occasion in which a 1960s spy series actually acknowledges that one of the genre's common "non-lethal" tropes, as it could potentially be in real life, is in fact lethal force.
"King Tut's Coup". While Tut and his henchmen are stealing a sarcophagus, one of the henchmen knocks out a security guard with a single blow on the back of the head with a club.
"The Unkindest Tut Of All". While Batgirl is confronting King Tut, his henchwoman Shirley sneaks up behind her and knocks her out by hitting her on the back of the head with a vase.
"Deep Freeze". When Mr. Freeze sends his henchman Frosty up to the roof to fix the TV antenna, Batman knocks Frosty out by hitting him on the top of his head.
"That Darn Catwoman". The title character's mooks take out Pat Pending and his valet with blackjacks.
Angels on Supernatural can do this by just touching the target.
In Dollhouse, Topher Brink uses the jaw-punch version to prevent Bennet Halverson from killing Echo.
Danger 5 spoofed this with Tucker declaring he was going to knock out a sentry for an hour, adjusting an egg timer on his wrist for that amount of time, then judo chopping the sentry.
Subverted on an episode of The Lone Ranger, where the Ranger knocks out Butch Cavendish with a punch to the jaw, but realizes he's faking when he examines him. He uses it as a way to set a trap and doesn't tell the guys with him that Cavendish is faking until later, when they're away from him.
How Edmund Blackadder and Lord Melchett are kidnapped in the Black Adder II episode "Chains". A German guard hits them over the head with a stick while they are distracted by another German guard.
Very common on Merlin, usually as a way for Merlin to use magic without Arthur seeing.
Horatio challenged a resident sadistic bully for a duel. Clayton feels shamed that a boy much younger than himself stood up to him, and is afraid that Horatio will be killed because said bully counts as one of the best shots in the Navy. Clayton therefore decides to knock Horatio unconscious and fight the duel in proxy as Horatio's original second.
The Indefatigable's crew take part in a night attack on a French ship. Archie Kennedy is having a fit which threatens to disclose their presence. Desperate Horatio taps him on head which solves the situation but leads to sad consequences, as the unconscious Archie is lost during their fight because the aforementioned bully untied the boat he was left in.
Both played straight and averted on Game of Thrones. In the first season, Tyrion is leading men into battle when he accidentally catches a warhammer to the head, and doesn't regain consciousness until well after the battle when he's being hauled around on a cart. However in the third season, it's played realistically, where a man who's clubbed unconscious wakes up after less than a minute. (Only to be clubbed again.)
In The Professionals this is the most common way of incapacitating someone. Doyle seems particularly prone to this, he is knocked out by a blow to the head at least three times.
Averted in Columbo, where a blow to the back of the head is a very common means of murder.
Red vs. Blue had this when someone would need a brief time unconscious.
Simmons: Ow, the back of my head! (then, later, Ow, the front of my face!)
In Jaga Jazzist's "Airborne" music video, an attempted murder is foiled when the gunman is knocked unconscious by a flying champagne cork.
In Flash Gordon, Aura uses this on Flash to let her father escape with Dale, so she can have Flash herself.
During the "Hit Cousin It" mode in The Addams Family, each shot to Cousin It is depicted with an animation of him getting hit in the head with a giant pinball.
In No Good Gofers, hitting either Bud or Buzz will show them getting clonked with a golf ball on the display.
Q*Bert is shown kicking a pinball off Ugg's head on the backglass of Q*Bert's Quest.
One of the animations in Transformers shows Mudflap getting hit with a pinball.
The bread and butter of the sport:
During standard matches, punches and blows to the head – e.g., kicks, punches and more complex moves – ordinarily will not "knock" a wrestler out, unless it is a finishing move, in which the wrestler can be rendered vulnerable for defeat for just seconds (such as the amount of time required to register a three-count pinfall) to longer, depending on the predetermined series of events. A wrestler can be "knocked out" to either sell a powerful move or sell the delivering wrestler's power.
"No Holds Barred" matches will similarly see wrestlers being able to absorb the force of blows from chairs and other weapons, possibly knocking out the targeted wrestler for a designated period of time. Usually, this is to allow the offending wrestler to complete an objective (such as doing something to humiliate his opponent) or demonstrate his power.
Sometimes, the knockout blows will be delivered during out-of-ring confrontations, such as to set up a feud. For instance, a heel wrestler sneaks up from behind of a face wrestler he's been heckling or targeting and bats him over the head with a club, knocking him unconscious.
In several versions of the Hero game rules, attacks made by surprise on an out of combat charater do double stun. If hit locations are used, attacks to the head have the highest stun multiplier, followed by attacks to the (other) vitals.
In the great pulp tradition, any combat in Spirit Of The Century, whether you're beating people up, stabbing them, or shooting them, can end in a knock out rather than death, and this is actually encouraged (for the GM, so the PCs don't all die before they can get stuffed in a deathtrap, and for the PCs so they can interrogate the Mooks they just clobbered).
Some d20-style games feature weapons that are designed to be non-lethal when used this way, such as the ubiquitous blackjack/sap in Dungeons & Dragons. A little questionable when you look at the weapon tables in Spycraft 2.0 and see that a 30lb maul does subdual damage.
Supplement The Asylum and Other Tales, adventure "The Asylum". Dr. Freygan could use his knowledge of human anatomy to perform a Star Trek style neck pinch and knock out a victim. Because he was a proto-shoggoth, he could extend his arm out many feet to do so.
The "Knockout Attack" rules allow something like this, with blunt attacks optionally allowing a Resistance roll (Damage vs. HP). If successful, the victim is knocked unconscious and takes 1/3 rolled damage. Assuming two average unarmed humans this amounts to a 10% chance...
Harder than usual because you can't do stun damage with regular unarmed attacks. People still lose consciousness by spending too long below zero HP, so you can fulfill the trope by doing that much damage, without causing any lasting injury by crippling a hit location. This means punching a guy in the chest several times is the most effective way to put him to sleep, if stunning weapons are unavailable.
If you actually try konking someone over the head, you probably will knock them out... because with much extra damage a head-shot does you'll shoot him straight into unconsciousness. And possibly right past a death check too. Presuming the straight hit point damage doesn't do it, he has to make a stunning/knockdown check at -10 if he takes any damage to his brain at all, and any botch (pretty likely at -10) knocks him out anyways. You have to buy a supplement to get the optional detailed injury rules that can leave the victim brain damaged afterwards.
A solar plexus shot (attack to the "vitals") does less bonus damage than a hit to the head, but it still does quite a bit extra, and has a stunning/knockdown roll at -5. So it probably will take them out, but they won't be unscathed...
Time Lord RPG (based on Doctor Who) main rules, "Curse of the Cyclops" adventure. If the Player Characters are captured they can be rescued by someone sneaking up behind the guards and knocking them out by hitting them on the back of the head.
Averted in the World of Darkness, where aiming for the head incurs a penalty to attack, but lets you do Lethal damage with weapons that otherwise do Bashing (stunning) damage. Hitting someone over the head could very well kill them.
Ars Magica has a rather abstracted combat system and two distinct methods of dealing non-lethal damage (The 'Scuffling' rules Core book, and the 'Bruises' system described in the 'Lords of Men' supplement). Neither method is especially likely to cause unconsciousness with a single blow, however, and both will leave the recipient with a 'residual' Medium Wound which imposes a -3 penalty to all rolls (and chance of worsening injury in response to strenuous activity) for at least the next 5-6 weeks of game time...
In the stage version of Les Misérables, Jean Valjean escapes from Javert at the end of "The Confrontation" by punching him out. Averted in the film version, where instead he escapes by leaping from a ledge into the sea.
The protagonist of the 1933 Broadway musical Pardon My English had two Jekyll & Hyde-like personalities which he would switch between whenever he was hit over the head.
Hitting the opponent in the head seems to be the most reliable way to knock someone out with no lasting consequences in BIONICLE. Ironically, the concept of Kanohi masks was introduced specifically so that characters wouldn't have to punch each other in the face, as they could weaken or disable the opponent by removing their mask. However, as the series got progressively Darker and Edgier, more "realistic" violence (with unrealistic consequences) was brought in.
Early masks were specifically designed so that they could be knocked off with a tap, and the toys were all designed to incorporate various punching or hitting functions. When the designers realized that kids weren't all that crazy for such play features, they made the connections sturdier and abandoned these gimmicks. This was around the time characters stopped targeting the masks in-story.
Claire Redfield is wacked on the head by a rifle stock from an umbrella security guard at the begining of Resident Evil: Code: Veronica and knocked unconscious.
Alpha Protocol uses the a variant of the karate chop... To the victim's exposed throat. It's an instant takedown. Other animations for non-lethal Back Stabs involve broken bones, dislocated necks, and chocking them until they fall unconscious. The game repeatedly lampshades how "non-lethal" does not mean "harmless": You can even see how much you cost people in medical expenses from recovering from the takedowns. Hey, it beats "orphans created", which you get for killing them.
Subverted if Mike pisses off Madison enough to make her try this on him. When Mike points out that it only works in the movies, Madison calmly throws a shock mine at him.
The Thief game series: attacks on unaware targets are more effective than those on alert targets. Hitting an unaware target with the blackjack will knock him/her out quickly and quietly. (If they're aware, they cannot be knocked unconscious but can take damage, although the attack is less effective than if they were unaware.) Though even if you use the blackjack(at least in the first game) when a guard finds an "unconscious" person they'll loudly announce that someone's been murdered. The intention might be to render them unconscious but for all you know you are delivering a lethal blow more often than not.
The Halo series rewards you for being covert - one melee strike from the back straight-up kills Elites that normally take several whacks just to get through their shields. Melee attacks in general are ridiculously powerful, as on most targets they have the destructive power equivalent to a good number of bullets. This is justified in that the player character - an armored super-soldier - is strong enough to reduce a man's skull to mulch with a single punch, and can FLIP TANKS.
In Halo 3, if you latch on to a Covenant Wraith, you can punch a hole through their armor.
However, in Halo ODST, the Rookie is unconscious for a whole six hours (by the impact of a very high altitude low opening crash) and then happily runs around New Mombassa. Perhaps his inability to speak is in fact resultant brain damage.
Or one mother of a headache brought on by a concussion.
Deus Ex made stunning attacks on unaware targets vastly more effective than those on alert ones. Hitting someone from behind with a baton or riot prod would knock them out quickly and quietly.
Trivia: Ionstorm Austin, the makers of Deus Ex, employed some of the Looking Glass Studios staff (who made Thief) when Looking Glass folded.
In Deus Ex: Human Revolution a vicious kind of Tap on the Head plays an important role as Adam Jensen can use his augmented strength to perform various non-lethal takedowns with punches to the head, chokeholds, or striking an enemy's head against a hard object (or striking the heads of two enemies together). Note 'non-lethal' here does not at all mean 'nobody gets hurt'; in the expansion, one NPC even calls you out, asking if you enjoy putting so many of her men into comas.
Splinter Cell. From Chaos Theory onward, Sam commonly uses the sleeper hold. He also uses punches to the back of the head and palm-strikes to the solar plexus.
The first game almost entirely relies on this trope being reliable though, you often do it in cases where you're not supposed to kill the people you're sneaking around.
Avalon Code ends Chapter 3 with Anwar using the "solar plexus" variant on your character. Heath uses the same variant at the end of Chapter 5 to keep you from getting the book out of a hijacked Valdo's hands.
The Shadowrun Genesis game uses the "solar plexus blow" variant as a distraction in which your character will stealthily pull it off then claim they had a heart attack to sneak into corporations as flavor text. This always works regardless of the unarmed combat and social capabilities of the main character.
Used in World of Warcraft as a Rogue ability called Sap which temporarily disables an enemy and does no damage.
And leaves them standing so their allies don't notice they're unconscious.note You act like their allies would notice if they were unconscious. Mobs in Warcraft cheerfully stroll over their comrades' bodies without noticing, let alone giving an alarm.
Rogues get a number of other kinds of stun attacks as well. It's hard to imagine how any of them is supposed to work in real life terms.
Except for Gouge. If you got stabbed in the eye, you'd most certainly stop whatever you were doing to just hold your hands over your eye and scream your head off, though arguably for much longer than a few seconds. And being hit again would do hardly anything to make you forget. You know, that you got ''stabbed in the freaking eye''.
Delita uses the 'sharp shot to the solar plexus' to subdue Ovelia while the latter was being kidnapped by the former in Final Fantasy Tactics.
Subverted in America's Army 3, melee attacks that hit the back of the neck are lethal.
In the Commandos games, the main point is to knock out the enemy mooks instead of killing them.
In Over Blood Raz gets knocked out in a single punch when Milly gets kidnapped.
And just moments before the second knockout, Musketeer Mickey gets a blow to the head by Musketeer Pete. Unlike with Sora, Mickey gets captured.
In the manga adaptation for Kingdom Hearts II, Sora punches the painting of Terra-Xehanort in frustration, causing it to topple on him and knock him out for a moment. The painting is destroyed as a result of going through him.
Subverted in The Saboteur with one of Sean's stealth kills. It involves some particularly hard and crunchy blows to the back of the enemy's head, and you can be sure they're as dead as if you neck snapped them instead.
How Link was rendered unconcious, so the Bulblins could take Ilia. It's never explained why they do this though.
Quest for Glory V introduces the blackjack as a Thieves-only item which lets them perform non-fatal sneak attacks.
Played straight in the Batman Arkham Series. Almost averted when Batman uses a blood-choke to silent take-down enemies, which as stated previously does have a low risk of permanent damage — but his opponents stay out for a very long time. His other method of 'knocking out' thugs involves no-holds-barred beat-downs where he snaps bones and most certainly gives severe concussions.
Not only that, but in Arkham City Batman himself is knocked out due to extreme blunt force trauma to the head no fewer than four times, two of which occur before he even puts on his mask.
Apparently averted in the first Resident Evil game. One ending variation has Barry Burton sneak up behind an unsuspecting Wesker and whack him on the back of the head with his magnum. This would have to kill Wesker for him to be able to transform into his undead, G-Virus self, present in the rest of the series.
Yuri from Tales of Vesperia does this with comical ease to multiple armored guards throughout the story, first with some thrown stones (That hit their helmets), then by casually hitting them in the back of the neck.
In Hitman: Blood Money, 47 can pistol whip someone that he had previously been using as a Human Shield. This knocks them out instantly and they stay out for the rest of the mission...unless someone finds them and shakes them a couple of times. Then they wake up immediately and with no apparent damage.
The stealth-based game Dishonored has the choke hold as a nonlethal option.
Metal Gear has this as well. No ill effects on the guards at all, either - as soon as they wake up after being choked out, they'll immediately be aware of what happened and alert the others.
Metal Gear Solid: The Twin Snakes has one particular cutscene where Snake is hit in the back of the head with a rifle stock, to which he responds by menacing the guy who hit him for about five seconds before falling over.
In Super Dangan Ronpa 2, this is how Mahiru Koizumi gets killed, as she dies by being bashed on the head with a baseball bat by Peko Pekoyama on the behalf of Kuzuryuu, whom he ordered Pekoyama to kill her because she covered up the death of his sister.
In Metro Last Light, a new 'takedown' system was added; sneak up behind an enemy, and you can either slit their throat, or poke them in the back then punch them in the face with your knife hilt when they turn around. This being a guaranteed knockout every time, non-lethal runs consist mostly of flitting around rooms in the shadows socking everyone in the face until every enemy is asleep.
Subverted in Narbonic. Mell clonks Titus Misanthropie with the butt of her gun... and he yells "Ow!" He then proceeds to give her advice:
Titus: Miss, you want to strike closer to the base of the skull. What is this, your first cold-cocking? Mell: Usually I just kill. Helen: Sorry, Titus. She's an intern.
This becomes a running gag during a DMFA arc, nicknamed "head-clunking." Then Aliyka tries it on Dan...
Done realistically in thisVG Cats strip. Yes kids, that is what you are going for when hitting someone hard on the head.
In Girl Genius, Oggie cures Lars' panic attack with a brick to the head. Og is a Jager and they are superhumanly tough, so by his lights this might be an acceptable form of discipline.
"Effective," perhaps; "acceptable," no. When Lars wakes up and asks about his rather obvious concussion Oggie claims a brick from the bridge flew wide and hit him. He even holds up the brick in question for proof.
Played realistically in Unsounded, when Quigley is knocked out by Starfish he's only out for a few seconds. As it happens in the middle of a fight, a few seconds is plenty.
Shadowhunter Peril has Bezaliel. When the angel first appeared he started spinning out in a psychotic episode and nearly overwhelmed everyone present with his messed-up mind, thanks to his empathy powers. The problem was solved by his confused son Nicholas picking up a large rock and smashing it on the top of his head, knocking him out instantly. This would become the solution for how to deal with Bezaliel for several days after, until they figured out what to do with him.
Family Guy makes fun of this trope in the episode where Peter steals the Popemobile; the guy guarding it tells Peter that "even the slightest tap on the head knocks me out. I always wake up feeling fine afterwards, but it's just so darned inconvenient." The fellow then demonstrates this by lightly touching his head and knocks himself out, allowing Peter to steal the car.
Stroker and Hoop has fun with this in one episode: The titular Stroker and Hoop knock out two guys to steal their clothes. One, though in pain, stays conscious and becomes despondent when he believes that Stroker had accidentally killed his friend with the blow to the head. After several moments of arguing ("Dammit, I know how to knock someone out!" "Well, do you check? Like, what if they have a concussion??"), the conscious man pretends to be unconscious just to avoid being hit again.
Dragoon: What is this, an episode of Gilligan's Island? Everybody gets hit once and they are instantly unconscious?
Red Mantle: Good one. Six bucks says he has amnesia when he wakes up.
One episode of SpongeBob SquarePants featured a health inspector getting knocked out in various ways over the course of the episode.
In the Star Wars: The Clone Wars episode Cloak of Darkness, the Badass Normal and The Mole single each other out. The Badass Normal knocks The Mole out cold with one right hook. Then, two seconds later, the prisoner knocks out Badass Normal from behind with a butt-stroke from a blaster rifle. (A butt-stroke is a hit with the back end of a rifle. Not what you think.)
Subverted in the American Dad! episode, "Stan's Night Out". Several people are hit on the head with bottles; they collapse, but don't lose consciousness, and they need to be taken to a hospital.
Pirhanor takes out Space Ghost with a wrench to the back of the head in "The Space Piranhas".
Jace knocks out the pirate One Eye with a wrench in "Space Sargasso".
Tarko the 12th Century Viking hits Jace over the head with a shield in "The Time Machine".
This happens quite a bit in The Simpsons, particularly to Homer, despite his characteristic hardheadedness. Also, in "Duffless," Homer repeatedly attempts to knock a defiant and drunk Barney out (to the point of repeatedly slamming his head in the car door) to get his keys and thereby prevent him from driving while intoxicated. He fails, and an annoyed and somewhat hurt Barney hands Homer the keys to get him to stop.
The "no ill effects" part of this trope happens to Rainbow Dash in the episode "Read It and Weep". After she crashes in the Cold Opening, we next see her waking up in a hospital bed with her wing in a cast and a band-aid on her head. To clarify: she was unconscious long enough to be taken to the hospital, ex-rayed, bandaged, dressed in a hospital gown and put to bed. Yet she suffers no brain damage whatsoever, and once she wakes up her broken wing is treated as the main injury, with her head injury completely ignored.
One episode of SWAT Kats has Razor knocked out by Callie with a vase to the back of the head, even though he's wearing a helmet at the time.
The Transformers: Humans and Transformers alike fall victim to this trope. Particularly Sir Wolfe after being whacked over the head with a stool by Nimue in A Decepticon Raider in King Arthur's Court.
As mentioned throughout, the tap on the head is not enough to knock someone out, and any hit on the head that does knock someone out is likely to have other effects. Boxers knocked out with a head shot frequently show signs of damage afterward, including confusion, memory loss, and other disorientation. There are multiple stories where boxers have apparently not realized that they were KO'd until someone else told them what happened, or cases where semi-conscious fighters have attempted to fight off medical help because they believe the fight is still going. You lose your memory from a few seconds before you fell unconscious. You would remember in this scenario being in the middle of a fight and then immediately being on the ground. This is why alibis that consist of "I was hit on the head and fell unconscious" are suspicious; if it knocked you unconscious you wouldn't remember it.
To give you an idea of how unpredictable a hit on the head can be, pro wrestler Mick Foley has one anecdote about his Vitriolic Best BudAl Snow, where Snow was supposed to be down and out for the count after being hit with a chair. Instead Snow popped back up to his feet, laughing in the face of the guy who hit him. This was done multiple times, with Snow popping back and laughing after each time. When Foley asked him about it afterward, Snow had no memory of the whole thing and claimed that he had been unconscious from the time of the first chair shot. Even with no longer having control of your faculties, one is far from guaranteed to quietly stay down.
The ultimate in "do not try this at home." Being hit on the head can cause concussion, and brain swelling which can lead to death, mental damage or health problems sometimes years down the road. Even more dangerous is the neck karate chop - although often played in TV and film for fun or as a way for a hero to save the day without killing anyone, if delivered improperly (or properly, depending on your point of view) it can cause neck fractures and even internal decapitation, and thus can be fatal. In other words, leave the "tapping on the head" to the stunt men and professional wrestlers, kids.
King Henry VIII of England was injured during a jousting tournament when he forgot to place his visor down. He was knocked unconscious and remained that way for a couple of hours. Although he managed to wake up, he reportedly suffered bad headaches and other health problems for the rest of his life.