Power Rangers: Especially in its first few seasons, the Rangers themselves were goody goods. Little to no negative behavior and all. But on occasion, Rita, Zedd or The Machine Empire would place a spell on the team or some members to cause problems (Such as Tommy debuting as an evil Power Ranger). Happened a good number of times. You'd Expect: That someone would attribute the odd behavior to a magic spell. Instead: The Rangers are dumbfounded by one of their own acting strange.
Mighty Morphin' Power Rangers, "The Green Candle": Rita has a candle that, when completely burnt out, will return the Green Ranger powers to her permanently. When Goldar captures Tommy, his presence causes it to burn faster. The Rangers set up a plan for Jason to hop through the portal. During the fight, a monster shows up and Tommy, not wanting to sit around, heads out in Dragonzord to confront it, but is quickly overpowered. You'd Expect: Jason needs a little more time - Either have Zack, Billy and Trini aid Tommy and form the Dragonzord Battle Mode or have the rest of the rangers form the Megazord without Jason, or thirdly, send another Ranger in to speed things up and get the candle out. Instead: Zack goes in and forces Jason into a Friend or Idol Decision which haunts the guy for years to come.
Another from Mighty Morphin, "Mighty Morphin Mutants": The monster, Commander Crayfish, and evil clones of the Green, Blue, and Black Rangers have undergone Make My Monster Grow and are fighting the Megazords. The Evil Rangers form a human chair and elevate Crayfish onto their shoulders, leading Billy to announce he's above their Blasters' range, leaving them sitting ducks. You'd Expect: Someone in this collective braintrust would think to disassemble the Megazord and let Kimberly take the Pterodactyl (which can fly) and use her individual blasters to knock Crayfish back down to the ground. And then finish him off with the Dragonzord Battle Mode. Instead: They keep barreling straight ahead, taking a few intense hits, then summon Titanus to simply overpower him (which worked, but still.)
From the season 2 premier, there's the rangers versus Pirantishead. The rangers meet the newly arrived Zedd's newest monster, and immediately summon their zords. Pirantishead freezes the triceratops, mastodon, sabertooth-tiger and pterodactyl zords on the spot. However, the T-rex is still unfrozen. You'd expect: The rangers would perhaps try and attack Pirantishead while he's doing this so they don't loose all their zords. Instead: They just stand there and watch as it takes control of the T-rex and sets it on them. And then it goes and does the exact same thing with the draonzord. Making this worse: for the next two episodes, at no point do the rangers seem to think shooting Pirantishead with their guns and disrupting his magic is an option, meaning he always manages to remain ahead of them.
From "A Ninja Encounter", there's this: Zedd has kidnapped Rocky, Ayesha, Adam, and their instructor, and put them in a cave with a magic snake which if it bites them will turn them completely evil. The Rangers goes to rescue them, but Zedd's sent down a monster to fight them. You'd Expect: The Rangers to just go in and save their friends from the snake, given they're right at the mouth of the cave, and they're not guarded, so saving the four shouldn't be difficult at all. Instead: They say there's "no time", and rush off to fight the monster, leaving their friends at the snake's mercy for the next two episodes. Making this worse: Once they beat the monster, they go back to rescue their friends, and it takes less than a minute to destroy the snake and free them. Yeah, real time crunch you got there, heroes.
In "A Different Shade of Pink" Rita and Zedd are sending monster attacks all over the city, causing Kimberly, who at this point in the series has lost her connection to her power coin, to pass out due to overexertion. In fact, she has a dizzy spell after the last fight in the episode, but she has to practice for the Pan Global gymnastics, so Tommy drives her to the Juice Bar at night. You'd Expect: Tommy would stay with Kimberly to spot her and make sure nothing bad happens to her. In fact, Tommy actually brings up this point, saying it's dangerous for Kimberly to be doing this alone. Instead: Kimberly tells Tommy that her coach will show up and he drives up. When Ernie tells her that her coach isn't going to make it, Kimberly does her routine on the balance beam anyway after everyone is gone, falling off, hitting her head, and winds upp being hospitalized. Making this worse: Kat is right outside the Juice Bar while Kim is practicing. It would be such an easy rewrite to have Kat be Kim's spotter, pushing her to not give up and overexert herself, then when Kat realizes what she's doing, it's too late and Kim fallls and hurts herself.
Power Rangers Zeo and possibly other seasons, "Mean Screen": This week's titular monster is actually winning against the Rangers. You'd Expect: That the Machine Empire would realize that the Rangers only have one weapon they haven't tried: the Zords. However, part of the Ranger code involves not bringing them in unless the monster is itself giant. With that in mind, by remaining at normal size, the monster can wipe out the Rangers in seconds. Instead: Klank and Orbus are sent in to Make Their Monster Grow, which leads to it being defeated by the Megazord like all the others.
Another from Zeo, the energy draining monster Main Drain feigns a surrender despite the fact that he was WINNING against the Zeo Megazord and even their powerful sword slashes were just doing Scratch Damage. You'd Expect: That the Rangers would instantly know something was up and that he could drain their power at any moment, realize it was a trap and take the opportunity to use the finishing strike on Main Drain, even though it probably wouldn't have finished him off based on the fact that it took TWO finishing blast barrages from the Red Battlezord to bring him down, it would have briefly stunned the monster, giving them time to escape before he could finish them off so they could go back, regroup, and find a way to win. Instead: The Rangers buy into the fake surrender, with only Kat realizing too late that it was a trap. By that time, Main Drain had burrowed a cable into the ground and drained all the Zeo Megazord's power, even breaking their sword in two (to that point a Megazord had never had its weapon broken), and it ended up draining the command center's energy in the process. If not for Alpha teleporting them out just in the nick of time, King Mondo would have won right then and there.
In Power Rangers Turbo, the final battle is this trope personified. Goldgoyle, a monster that defeated both Megazords, was sent only to distract them so Divatox could launch an all out attack on Angel Grove. You'd Expect: A quick and hasty retreat once they realized they were getting their asses royally kicked, as the monster showed no indications of attacking Angel Grove or the power chamber. They'd ward off the attack by the Piranatrons while figuring out Goldgoyle's weakness, go back, and take care of business. Instead: They respond by self-destructing the Rescue Megazord, using a special superpowered version of the Turbo Megazord spinout (which does not finish off the monster), then suffer damage to where the Turbo Megazord is inoperable, losing both Megazords while giving Divatox time to attack. The events that were leading to the best season of all time, Power Rangers in Space, but still.... But to be fair: at this point, the Rangers were under a tremendous amount of stress, especially with Zordon and Eltar under attack and feeling a lot of anxiety and helplessness about it (Dimitria, on Zordon's orders, tells them that they can't leave Earth to help, in spite of the news) which really didn't help boost their morale. And probably because of the amount of pressure, they were not thinking straight and didn't take the time to asses the situation more carefully, which they normally would have done considering how they had TJ as their leader who is usually level-headed and cautious.
As if that wasn't already bad enough, Divatox and Elgar lead an army of Piranatrons to completely wreck the Power Chamber. You'd expect: On their way to try and aid Zordon and Eltar, Dimitria and the Blue Senturion could have at least taken the Rangers with them when they clearly were already exhausted from their bittersweet defeat of Goldgoyle and saw how badly that went down. And with that, they probably should have also just shut down the Command Centre for good measure, take anything important out of there, and then just abandon it as they go out into space. Why? Well, with Zordon gone, it looked like the security of that place went down a notch. Also, Dimitria is not as powerful as he is. And besides, all of them will probably be seen teleporting out of the place so it's highly likely that the villains would have followed all of them on their way out to go to space anyway (and in turn, the Rangers would fight them off for bit on the way, which is enough to defend the Earth considering that Eltar had already fallen by then — meaning that Divatox and co. would probably get called on soon to help with the destruction of Eltar); also, with an abandoned Command Center/Power Chamber, it wouldn't matter if it got trashed and the Rangers — if they had just gone with Dimitria and the Blue Senturion, that is — would probably get to Zordon faster. Instead Dimitria and the Blue Senturion just leave without them and the Rangers are left to fight a seemingly never-ending onslaught of Piranhatrons. They are also told to, once again, stay and defend the Earth. And the Power Chamber gets destroyed in an onslaught that they just didn't have the energy for...
On that note, in an earlier episode, General Havoc's special zord, the Metallosaurus. You'd expect: The Turbo Megazord to jump out of the way of the sword-breaking tail slash and use the second, very powerful finisher used on Goldgoyle where it doesn't just spinout slash but launches itself through the monster, which would have undoubtedly defeated Metallosaurus with no problem. Instead: They let it break their sword and get their asses kicked.
In another episode, Divatox and Co. have stolen The Phantom Ranger's Phantom Ruby and now, he's close to death. The Rangers are at a loss until they decide to bring Divatox's Space Base down to Earth with a Giant Magnet. Their magnet successfully starts dragging the base. Divatox orders Porto to call up a Monster of the Week to deal with the problem. You'd Expect: Porto to send down a monster well-equipped to dealing with giant magnets. Instead: Porto summons a robot monster called Metal Mangler, who lasts all of five seconds before the magnet drags it to Earth. His second choice, Crosspatch, is not a robot, so he's much more successful.
In the final episode of Power Rangers Lightspeed Rescue, Carter Grayson has just thrown Queen Bansheera into the tomb that she had attempted to use to bring the Demons from the Shadow World into the real world. You'd expect: For Carter to close the lid on the tomb, thus ensuring that she will never return. Instead: He neglects to close the tomb, turns around to give a thumbs up to Ryan, and it leads to Bansheera grabbing him, pulling him into the tomb and attempt to pull a Taking You with Me. Thankfully: Diabolico arrives in the nick of time to save Carter.
Wes is forced into a 10-Minute Retirement by his Identical Grandson, Alex, who takes over his position as Red Ranger. Prior to this, Alex watched all of the rangers battles in his Mission Control, so he knows what their weapons and zords can do. When Frax unleashes his new robot, Dragontron, the team brings out their Shadow Force Megazord and its BFG. They get a clear shot, and... You'd Expect: Shoot him now! Shoot him! Instead: Alex has the team hold their fire. This allows Frax to warn his robot, thus ruining the shot and resulting in a battle in which Frax and the robot clear out. For extra points: He yells at the rangers and blames them for failing the mission when they just followed his orders to the letter.
In the next battle with Dragontron, the Megazords get disabled by Frax's new Energy Siphon. To remedy this, the Rangers go after Frax and the Siphon. After clearing out Frax's Cyclobots, they corner the robot villain. You'd Expect: Alex would have a few Rangers pin down Frax while the rest disable the Siphon. Instead: Alex orders the Rangers to disregard Frax and go after the Siphon. While the Rangers question the logistics of this decision, Frax gets up and uses the Siphon on them. Left defenseless, the Rangers are saved by an unmorphed Wes, who takes out the Siphon by himself.
Power Rangers S.P.D. "Recognition", in a plot recycled wholesale from Tokusou Sentai Dekaranger: The Rangers have seized an alien criminal who wiped out ninety planets off-screen (a burglar in Dekaranger) and additionally can swap bodies with others - but can't speak English (or Japanese in Dekaranger) without a translation device. The commander wants him brought in for questioning. You'd Expect: When escorting a potentially dangerous criminal, multiple Rangers should be escorting the guy to his cell, just in case. Instead: The Blue Ranger does it alone and falls victim to the alien's body swapping, and when the alien destroys the translator, he is left in no position to stop him. The alien, in the Blue Ranger's body, takes control of the Delta Base and even authorizes the Ranger's execution. Additionally: Especially stupid in SPD, as the Rangers regularly capture alien criminals in cards, and there's no real reason not to use them to transport the prisoner here. Dekaranger doesn't have this problem as they don't have capture cards; they're usually authorized to use lethal force instead.
Power Rangers Jungle Fury has the Rangers trapped in a TV game show. Unfortunately, the show is being run by the bad guys who are saying Screw the Rules, I Make Them!, with half the Rangers being eliminated from the game for petty rules violations (and of course, if they lose, the villains will have free reign to eliminate mankind). The host offers the Rangers the chance to give up some of their winnings for a trip to Hawaii. You'd Expect: The Rangers remember that not only are cash prizes at stake, but also the fate of the human race, so they shut up and keep playing. Instead: Lily jumps at the chance, claiming she's always wanted to go to Hawaii. For that, she not only loses some cash from the pot, but she's thrown out of the game as well.