History Main / CavalryBetrayal

'''Wounded civilian:''' [{{Beat}}] Oh no, it's the Catholic Church.

* The famous [[WhamEpisode Wham Level]] of ''VideoGame/ModernWarfare2'', "Loose Ends", ends with the team holding a cabin against an endless stream of attackers while a huge amount of data is copied on a portable hard drive and most of them are dead when all of the data is secured. The last men make a frantic dash down a hillside without any real cover while under fire from lots of automatic rifles, machine guns, and rocket launchers and just 14 meters from the extraction point the player gets downed. When you regain consciousness a few seconds later, your last teammate Ghost drags you by your jacket and finally helicopters of Shadow Company appear from behind you and mow everything down with their miniguns. And when you finally stumble the last steps to the evac chopper, General Shepherd takes the hard drive and shoots both you and Ghost in the chest. The last thing you see is your bodies being thrown in a ditch, a soldier emptying a gas canister over you, and Shepherd throwing his burning cigar at your face, all the while Price is yelling on comm about how the rest of his team is under attack by Shepherd's men and imploring them not to trust Shepherd.

* Parodied in the Anniversary Brawl between the cast of Website/ThatGuyWithTheGlasses and WebVideo/TheAngryVideoGameNerd when Benzaie shows up, and everyone else who sides with the Nerd over the Critic.

* ''WesternAnimation/TotalDrama'': [[spoiler:After getting picked as Bowie's helper in the final challenge, [[Characters/TotalDramaJulia Julia]] wastes no time wasting time and is an absolute hindrance to him as revenge for eliminating her last episode. She even blackmails him into signing a legally-binding contract that stipulates he'll fork over half of the million to her if he wins in exchange for her cooperation, only to abandon him once he terminates the contract and also takes the saw away for good measure.]]

* The IncitingIncident of ''Literature/TheDinosaurLords'' is Jaume being ordered to perform this on Karyl, whose forces are being slaughtered by their common enemy. He charges towards Karyl's forces, making it seems as if he's going to rescue him, only to send the blast od hadrosauruses' [[MakeMeWannaShout sonic attack]] towards him, crippling Karyl's defence and ultimately leading to man's (first) demise.

* The Battle of Bosworth Field. The Stanleys, nominally allied with King Richard III, waited until he was separated from his army and charged the King's Bodyguard in the rear.

* The U.S.M. ''Valor'' in 'VideoGame/DeadSpace1''. Initially believed to be on a rescue mission, is later heavily implied that they were full aware of how dire the situation was on the U.S.G. ''Ishimura'' and that they would have rather nuked the whole ship than even bother with trying to save anyone.

* The U.S.M. ''Valor'' in 'VideoGame/DeadSpace''. Initially believed to be on a rescue mission, is later heavily implied that they were full aware of how dire the situation was on the U.S.G. ''Ishimura'' and that they would have rather nuked the whole ship than even bother with trying to save anyone.

* Wrestling/{{WCW}} Bash at the Beach '96, which in turn precipitated the biggest FaceHeelTurn in pro wrestling history. After Wrestling/{{Sting}}, Wrestling/RandySavage, and Wrestling/LexLuger had taken a beating from The Outsiders (Wrestling/ScottHall and Wrestling/KevinNash), Wrestling/HulkHogan comes down to the ring, ostensibly to [[BigDamnHeroes help out Sting and Savage]] (with Luger having been knocked out)... and then leg-drops the fallen Savage, revealing himself to be the Outsiders' mystery partner and heralding the beginning of the Wrestling/NewWorldOrder.

->'''Maxwell:''' Yes, my fellow Christians, we have come to save you...
->'''Wounded civilian:''' Hooray, it's the Catholic Church!
->'''Maxwell:''' [[SuddenlyShouting FROM YOURSELVES!]]
->'''Wounded civilian:''' [{{Beat}}] [[KnightTemplar Oh no, it's the Catholic Church.]]
-->-- WebVideo/HellsingUltimateAbridged

->''"Death to the Scourge! And '''death to the living!'''"''
-->-- '''Grand Apothecary Putress'''' WhamLine before destroying a united Horde and Alliance force at the Wrathgate, ''VideoGame/WorldOfWarcraft''

* Wrestling/{{WCW}} Bash at the Beach '96, which, in turn precipitated the biggest FaceHeelTurn in pro wrestling history. After Wrestling/{{Sting}}, Wrestling/RandySavage, and Wrestling/LexLuger had taken a beating from The Outsiders (Wrestling/ScottHall and Wrestling/KevinNash), Wrestling/HulkHogan comes down to the ring, ostensibly to [[BigDamnHeroes help out Sting and Savage]] (with Luger having been knocked out)... and then leg-drops the fallen Savage, revealing himself to be the Outsiders' mystery partner and heralding the beginning of the Wrestling/NewWorldOrder.

* Wrestling/MattHardy running down to ringside with a chair during his brother Wrestling/{{Jeff|Hardy}}'s match with Wrestling/{{Edge|Wrestler}} at the 2009 Royal Rumble. This one still managed to surprise because Matt had legitimate gripes with Edge, and even if you did not know that, Edge had sent Matt packing from Monday Night Raw after stealing his girlfriend (well, Kane stole her first but we digress).
* After [=BxB=] Hulk became [[Wrestling/DragonGate Open The Freedom Gate]] Champion, Davey Richards, who lost in the first round of the tournament to decide who would be holding the title, ran out to attack him. The surprise here was that it was Richards' opponent, Yamato, seemingly coming out to stop him only to join Davey's attack.

* In Season 4 of ''Series/{{Lost}}'' A boat arrives, that the castaways believe is going to rescue them, but in fact brings a team of mercenaries with orders to kill Ben and anyone who gets in their way. Some of them do get rescued anyway, but it doesn't help.

* ''Film/RevengeOfTheSith'': The 41st Elite Corps, led by Master Yoda is sent to Kashyyyk to repel [[MemeticMutation the droid attack on the Wookiees]]. But then Order 66 is issued and the clones, Gree and Jek, turn against Yoda though he beheads them before they could lay a shot into him due to the Jedi Master [[MySignificanceSenseIsTingling sensing the deaths of his fellow Jedi via the Force]]. Chewbacca and Tarfful help Yoda escape Kashyyyk, and despite the Separatist forces under General Linwodo [[LetNoCrisisGoToWaste taking advantage of Order 66 putting the Republic forces in disarray]], the Clones under Faie regrouped and defeated the droids, though most of the Wookiees are captured by the clones and enslaved by the newly-created Galactic Empire.

* In ''Film/WildWildWest'', Not exactly in combat, but Arliss Loveless promises Bloodbath [=McGrath=] and his men assistance in reviving the cause of the Confederacy. As his men wait to meet up with their support, a tank rolls up and opens fire on them. An especially cruel example, as his only reasons seem to be testing out his new weaponry, and getting revenge on his former comrades for surrendering at the end of the Civil War.

* Happened to Lieutenant Mower, the first of the Cyberpsychos you will likely deal with in ''VideoGame/Cyberpunk2077''. One of Militech's special agents, she was experiencing some problems and just wanted some help and some treatement. But instead, Militech sent in a hit squad to kill her, labeling her a cyberpsycho and declaring her untreatable. Unfortunately for the agents, her skills as an agent and the combat-grade cyberware she was implanted with proved to be too much for the soldiers to handle.

* ''LightNovel/BakaAndTestSummonTheBeasts'' gives us the "FFF". On the one hand, they'll help out in summon wars just as much as the next student in the class. On the other hand, if they so much as hear rumors that a girl's been even relatively nice to you...

* Poor Raphtalia had to endure this in her Backstory, which is fully explored in Episode 15 of ''LightNovel/TheRisingOfTheShieldHero''. After losing her parents in one of the Waves, she tries to keep everyone's spirits high, and even gets them on the road to rebuilding their town. A force of knights arrive that everyone initially thinks is going to help them. '''They're not.''' They're there to slaughter all the remaining adults and sell all the kids as slaves, which leads directly to Raphtalia's hellish ordeal under the sadistic lord she was enslaved to before meeting Naofumi. To say that this experience [[BreakTheCutie broke her]] would be an understatement.

* Happens to the bad guys in the second ''Literature/TheHeroesOfOlympus'' book. The giant Polybotes is leading an army of monsters against New Rome, and he's pleased to see the [[AmazonBrigade Amazons]] (whom he had earlier tried to bring over to his side) coming to join the battle. Turns out they're here to help the Romans.
* In ''Literature/{{Animorphs}}'', this is a common role played by the Andalite military: The final book has the Andalites ready to destroy the human race rather than let it become a [[PuppeteerParasite resource]] used by [[TheEmpire the conquering Yeerk Empire]]. Earlier books had other Andalites with plans was based on the same [[WellIntentionedExtremist well-intentioned extremism]]: Arbat, who was probably just a rogue faction rather than representing the Andalites in general; and Alloran, who developed a biological weapon to eliminate the alien race of Hork-Bajir.
* The IncitingIncident of ''Literature/TheDinosaurLords'' is Jaume being ordered to perform this on Karyl, whose forces are being slaughtered by their common enemy. He charges towards Karyl's forces, making it seems as if he's going to rescue him, only to send the blast od hadrosauruses' [[MakeMeWannaShout sonic attack]] towards him, crippling Karyl's defence and ultimately leading to man's (first) demise.
* In ''Literature/ATaleOfTwoCities'', soldiers arrive during the siege of the Bastille only to turn their guns against its defenders.
* ''Literature/ShadowPolice'': In ''The Severed Streets'', Quill is being pursued by the Ripper. Neil Gaiman arrives to pick him up in a car and spirit him away. However, he is actually there to deliver Quill into an ambush.
* ''Literature/TheCrimsonShadow'': A rare [[InvertedTrope inversion]]. During a naval battle between the Avonites and Eriadorans, ships come sailing over from Baraduine (an island ruled by Avon), making the former celebrate. Instead though they attack the Avonite ships, since it turns out that Baraduine would like to be free from their rule.

* In the backstory of ''Literature/ShadowOfTheConqueror,'' [[EvilOverlord Dayless]] had an alliance with the nation of Lourane when he was waging his wars, and the two were on course to split [[FloatingContinent Tellos]] between them. However, Dayless wanted to conquer ''[[TakeOverTheWorld all the world]],'' and so eventually betrayed Lourane in this manner. This backfired on him, as it led to Lourane [[EnemyMine forming an alliance with their longtime enemies]] in order to defeat Dayless and destroy the Dawn Empire.

* The priceless ''Series/StarTrekVoyager'' episode "Message in a Bottle". The ''Prometheus'' is getting trashed by Romulans when some Starfleet ships arrive, only to attack everybody, since as far as they know, it's still under Romulan control. It doesn't help that the [=EMHs=] accidentally fire a torpedo at a ''Defiant''-class ship (they were aiming for the Romulans, but missed).

* A heroic example comes in the season 3 finale of ''Series/TheLastKingdom''; [[spoiler: having promised [[TheResenter Aethelwold]] that he will lead his cavalry in a rear attack against the forces of Wessex when they're locked in battle with the Danes as part of Aethelwold's plan to kill his cousin King Edward to seize power, when the time comes, Lord Sigebriht of Kent chooses to remain loyal and attacks the Danes instead. His actions turns the battles in the favour of Wessex, [[RedemptionEqualsDeath but Sigebriht is killed in the fighting]].]]

* In ''VideoGame/HalfLife1'', the [=HECUs=] sent in to quell the alien invasion of Black Mesa are also there to contain all information of the outbreak by killing every Black Mesa employee they meet, and that includes the PlayerCharacter, Gordon Freeman. Some aren't happy about the job, others are. Whatever it is, it gets justified quick when they come to think that Gordon is a psychopath (due to how [[OneManArmy Gordon by that point has been singlehandedly slaughtering scores of their buddies]]) and responsible for the whole mess in the compound. They get some karmic justice in the add-on ''Opposing Force'', where the [[DoomTroops Black Ops soldiers]] deliver them their own Cavalry Betrayal.
%%* Also performed in ''VideoGame/TheyHunger''. (ZCE)

%%* The twist toward the end of ''VideoGame/MegaManXCommandMission.'' (ZCE)
* The Komato in ''VideoGame/{{Iji}}'' combine this with AlwaysABiggerFish. They're there to kill the Tasen, but you're... well, there.
* In ''VideoGame/WorldOfWarcraft'', the battle of Angrathar contains a genuine example of TheCavalry when Horde wolf-riders charge into battle to help the beleaguered Alliance. But when the [[BigBad Lich King]] himself emerges, Putress bombards the entire battleground with [[DeadlyGas Blight]], Horde, Alliance, and Scourge alike.
* The famous [[WhamEpisode Wham Level]] of ''VideoGame/ModernWarfare2'', "Loose Ends", ends with the team holding a cabin against an endless stream of attackers while a huge amount of data is copied on a portable hard drive and most of them are dead when all of the data is secured. The last men make a frantic dash down a hillside without any real cover while under fire from lots of automatic rifles, machine guns, and rocket launchers and just 14 meters from the extraction point the player gets downed. When you regain consciousness a few seconds later, your last teammate Ghost drags you by your jacket and finally helicopters of Shadow Company appear from behind you and mow everything down with their miniguns. And when you finally stumble the last steps to the evac chopper, General Shepherd takes the hard drive and shoots both you and Ghost in the chest. The last thing you see is your bodies being thrown in a ditch, a soldier emptying a gas canister over you, and Shepherd throwing his burning cigar at your face, all the while Price is yelling on comm about how the rest of his team is under attack by Shepherd's men and imploring them not to trust Shepherd.
* Likewise in ''VideoGame/FireEmblemGenealogyOfTheHolyWar'', although the lead-up makes it a bit easier to see it coming. Chapter 5 looks like it's going to be the final battle against all of the antagonists, but rather unexpectedly Velthomer switches sides and starts attacking Freege's army as soon as you get close to Velthomer, double-crossing its allies. All this in spite of the fact that Arvis has now been revealed to be in league with the Loptyr Sect. The chapter ends with Sigurd being led to Belhalla, ostensibly to be cleared of all charges, only to learn that he is still labeled as a traitor and will be killed, along with much of the party (though their fates are mostly left ambiguous).
** Its interquel ''[[VideoGame/FireEmblemThracia776 Thracia 776]]'' features a sort-of Meta example: late into a grueling defence chapter, an army of green (NPC) Thracian Dracoknights arrive and start heading for the city. The player will probably be exclaiming "I'm saved!" at this point, as the {{Non Player Character}}s fly in and clear out the enemies. Until they actually reach the city, upon which they start attacking ''you''. Turns out, they're on ''neither'' side: they just want the city back under their control, meaning you're just as much of an obstacle to them as the enemy army. Notable in that it's possibly the only time in the entire series where green NPC units can actually attack you.
** [[VideoGame/FireEmblemShadowDragonAndTheBladeOfLight In the original game and its remake]], Marth's father, King Cornelius of Altea, was killed during the invasion led by Medeus, when the army of Gra, who was supposedly allied with Altea, betrayed them and attacked them from the rear.
** ''VideoGame/FireEmblemAwakening'': In Chapter 17 some of your allied forces infiltrate the enemy fort partway through the battle, but Excellus quickly appears and sways them to his side, via holding their families hostage.
** In ''VideoGame/FireEmblemThreeHouses'' provides an example happening to the ''enemy''. On the Crimson Flower route, during the battle for the Great Bridge of Myrrdin, the enemy commander Judith of House Daphnel receives Leicester Alliance reinforcements led by the noble Acheron, who has been noted for being a DirtyCoward and conveniently spawns near the exit to the map away from the majority of the reinforcements. Should Byleth and the Black Eagle Strike Force strike down the majority of said reinforcements (including their general), he will abandon Judith and leave with his personal guard to save his own hide, which prompts her to [[KnowWhenToFoldEm order the remaining Alliance soldiers to retreat]] (and unfortunately for her, [[ButThouMust it's mission-critical to kill her before she escapes]]).
* There's a Japanese DOS-era tactical RPG called ''Legend of the Seven Heroes 2'' that ends like this. After a ClimaxBoss battle against the enemy nation's BigBad General and his army, an army from the friendly nation shows up, and the main character assumes they're there to rescue them. However, the friendly nation's General arranges a truce with the BigBad General and decides to kill the main characters, because he figures that the main characters' survival would bring peace between the two nations and thus be politically disadvantageous to both of them. The final battle of the game thus has your 7 characters being attacked from the North of the battlefield by the BigBad General and his army and from the South of the battlefield by the not-so-friendly nation's General and ''his'' army.

* An extremely rare ''villain'' version happens in ''VideoGame/AssassinsCreedBrotherhood'', during Sequence 8, where after destroying all of Cesare Borgia's support, he sees one last chance in his Papal Guard army arriving at Roma's gates, only for them to arrest him on orders of the new Pope.
* After the finale of ''VideoGame/Left4Dead'', the characters are rescued by the military in an APC. The subsequent comics show that the army locked them up out of fear that they were carriers and intended to kill them before a horde rush allows them to escape.
* In ''VideoGame/YsSeven'', after getting the last crest from the Sea Dragon on Ruin Island you go back to your ship only to be attacked by a giant Titano, Just in the nick of time the Dragon Knights show up and Save you. That is only half true however, They are actually here to rescue Aisha and Arrest you for "kidnapping" her and assassinating the King who was murdered mere moments after Adol leaves said King's bedroom.

* The American soldiers and pilots in ''VideoGame/DesertStrike'', who are stranded behind the enemy lines and waiting for the player to rescue them, aren't exactly immune to friendly bullets.
* Happens in ''VideoGame/CommandAndConquerTiberiumWars'' when Killian's reinforcements turn against Nod's Temple Prime. ''Kane's Wrath'' reveal that it was actually Alexa who ordered LEGION to pretend to be at the head of Killian's forces.
-->'''Kane''': "Of course I could not have planned for an ambush BY MY OWN FORCES!"
* In ''VideoGame/DeadRising'', if the player follows the path to the best ending, the heroes will call for help. What they get, instead, is a spec ops squad come to ensure the truth behind the zombie outbreak remains a secret, and everyone is fair game, living or undead.

* ''VideoGame/PokemonSunAndMoon'': Wild Pokemon will sometimes call for help if they are losing a battle. Usually this help arrives in the form of another member of their own species, more rarely a Pokemon of another species will show up. And sometimes, their ''predator'' will show up, and attack the Pokemon that called for help.
* ''VideoGame/Persona5'' opens up with an inversion. The protagonist acts as the cavalry and rescues a woman from a drunk harasser, only for him to pull out some dirt he has on her and convince her to testify that you randomly beat him up.
* In ''Franchise/TheElderScrolls'' series' backstory, King Joile of Daggerfall convinced Gaiden Shinji, the legendary Redguard hero and leader of the [[TheOrder Order of Diagna]], to join him in the Siege of Orsinium (the home city-state/fortress of the [[OurOrcsAreDifferent Orcs]]). Joile then convinced Shinji, the [[MasterSwordsman Blademaster]] and founder of the Imperial City [[GladiatorSubquest Arena]], to participate in a CombatByChampion DuelToTheDeath against the Orc leader, Baloth Bloodtusk. As Shinji and Baloth were fighting, Joile ordered his archers to open fire on both of them. As it turned out, Joile not only wanted to sack Orsinium, but planned to invade Hammerfell after and knew that Shinji would have been a major obstacle. (Joile would get his comeuppance, dying during what would be a failed invasion of Hammerfell.)

* The PlayerCharacter themselves can do this in ''VideoGame/PathfinderKingmaker'' during the Kellid invasion. Your patron, Lady Jamandi Aldori of Restov, goes to fight them and [[GondorCallsForAid calls for your army to join her]], but you can choose to go chasing after Tristian instead (which is required if you want to complete his RomanceSidequest). Should you do so, you'll finally arrive to discover the opening rounds have already happened and ended in a PyrrhicVictory for Restov: the Kellids have been stopped for the moment, but Jamandi's army is shattered and her adoptive son Kassil died fighting in her bodyguard, and you're in for a ''vicious'' WhatTheHellHero from Jamandi herself.
* A villainous example happens in the third ''VideoGame/GalaxyAngel'' game. Tact defeats Rowil of the Valfask, but takes notice that a fleet of enemy reinforcements suddenly turned around and left him to die, which leaves the heroes unsettled about it. After [[spoiler:Wein]] reveals his true colors, [[KlingonPromotion he takes command of those remaining forces]].

* Inverted in ''WebVideo/CounterMonkey''. During the ''TabletopGame/ThievesWorld'' campaign, the players attacked a cult and the DM expected that they would need help by their employer, Tempus Thales, who came with six guardsman to serve as backup. However, TheCavalryArrivesLate and the party wins the day without assistance. When they heard approaching troops, they assumed it was more cultists and ambushed Tempus as he entered the room, inflicting FacialHorror and driving the campaign OffTheRails in the process.
* Much like [[Manga/{{Hellsing}} the source material]], the Catholic forces in ''WebVideo/HellsingUltimateAbridged'' are being mowed down en masse by Dracula's forces. Unlike the source, however, the Papal Knights are nowhere in sight, the forces under Bishop Enrico Maxwell being comprised of fringe factions, the KKK, and the Sacred Order of the Temple Beth Zion. The last of these take the hardware Maxwell gave them and leave, leaving the extremists, the Klansmen and Maxwell to their fates.

* In ''WesternAnimation/ReBoot'', this was part of [[BigBad Megabyte's]] [[TheChessmaster grand strategy]] during the Web World War: he waited for Mainframe's CPU fleet to take heavy casualties before deploying his own forces, and the moment the invasion ended, he immediately directed his troops to destroy the city's remaining defenses. It was this betrayal that ultimately allowed Megabyte to conquer Mainframe.

* In the three part second season finale of ''WesternAnimation/BeastWars'', Cybertron dispatched agent Ravage to prehisotric Earth to aid the Maximals in capturing Megatron. However, Megatron was the only one who knew that, rather than take them back to Cybertron, Ravage was going to terminate all the Maximals and rogue Predacons. Even worse, Megatron used a secret message from [[WesternAnimation/TheTransformers his predecessor]] to convince Ravage to side with him and attack the Maximals.

* ''Anime/ReadOrDie'': It's already been suggested that the British Library has a secret agenda, but the full extent of it isn't clear till they show up in force.
* In the first episode of Anime/{{K}}, our hapless protagonist, Yashiro Isana, is being chased by people who want to kill him-and he has no idea why. He is saved by a total stranger, Kuroh Yatogami who just wants to kill Yashiro himself.
* A rare example of this happening to the antagonists shows up in ''Anime/MobileSuitGundamSEEDDestiny'' when [[BigBad Chairman Durandal]] tries to reinforce his game-ending super-weapon by bringing up the Home-guard. However, the Calvery in this case happened to be lead by veterans of the [[Anime/MobileSuitGundamSEED previous war]] who'd had enough of [[WellIntentionedExtremist Extremists]]. A few minutes after entering the battle they switch sides, taking a good chunk of the [[BigBad Big Bad's]] forces with them.
* ''Anime/NinjaScroll'': Despite what he said earlier about the wisdom of remaining neutral, the lord of the Mochizuki clan turns up with his forces to help the protagonists take on the Devils of Kimon. But when Kagerou reports to her lord, he runs her through with his katana, as he's actually the BigBad.

* In ''AudioPlay/SaintBeast'', Goh, Shin, Rey and Gai turn against Luca and Judas at the moment they are most needed due to {{brainwashing}}, which isn't lifted until it's too late. Then, after Judas and Luca are banished to hell the others plot to free them with the help of the Goddess. The Goddess, however, is plain old sick of fighting and sells them out to Zeus. They get TakenForGranite and have their souls sealed away in darkness. And Judas and Luca are still stuck in hell.
* ''LightNovel/BakaAndTestSummonTheBeasts'' gives us the "FFF". On the one hand, they'll help out in summon wars just as much as the next student in the class. On the other hand, if they so much as hear rumors that a girl's been even relatively nice to you...
* In ''Manga/OnePiece'', during the Arlong arc, after being under Arlong's thumb for eight years and all Marines attempts to save them had been blockaded by the Arlong Pirates, Cocoyashi Village finally had marines reach the island...only for them to be there to confiscate Nami's money, preventing her from buying the village from Arlong.

* ''Anime/GreatTeacherOnizuka'':
** In the first episode of the anime. When the three punks who try to blackmail Onizuka are gloating about how much money they're about to get, they accidentally anger a large group of [[UsefulNotes/{{Bosozoku}} biker thugs]] who are going to wreck them for their arrogance, when Onizuka shows up and punches his way through the crowd, cowing the bikers who recognise his fearsome reputation. The students are practically crying with relief at being saved by their teacher, only for Onizuka to declare none of the bikers can touch them... because [[LeaveHimToMe they're his prey]].
** ZigZagged later on in Episode 8. After his students at another school have pranked him (by gluing his fingers to bowling balls) and run off, they also find themselves threatened by a gang. Onizuka shows up and at first seems to refuse to help, even going so far as making them bungee jump off a bridge to prove their manliness. However, he then punches all but one of the gang members off the bridge, and DrivesLikeCrazy after the last one (in the vice principal's PreciousPreciousCar).

* ComicBook/{{Crossed}}: During the onset of the Crossed apocalypse in the United States, a Navy fleet from Pearl Harbor was send with the objective of protecting the cruise ships that would evacuate all the surviving civilians located at San Diego, California. Unfortunately, the fleet somehow fell victim to the infection and instead opened fire at the harbor, destroying the ships and massacring hundreds or possibly thousands of survivors.

* The Gurkhas do this to Sasha in the ''WesternAnimation/KimPossible'' fic ''Fanfic/NightsInTheBigCity''.
* In the ''Franchise/LyricalNanoha'' fanfic ''[[Fanfic/TeanasTravels Rise of the Phoenixes]]'', :Jane Smythe does this to Miles Fairbrass and Harry Henriksen.

* In the ''WesternAnimation/LiloAndStitch''[=/=]''Franchise/StarTrek'' fanfic ''[[FanFic/StarlightSeries Starlight]]'', Jumba initially thinks Experiment 628 has come to save them, until he reveals his allegiance to the Borg.
* In ''Fanfic/TheSwarmOfWar'', the Space Marines, twice. First, the ones woken up as a SuperweaponSurprise turn out to be largely corrupted by Chaos. Later, during a battle between the King’s Army and the Chaos, forces led by the Loyalist Space Marines attack and wipe out the Chaos… and then the other side; due to the King refusing to recognize the Space Marines as his superiors, his kingdom is branded as heretics.

* Inverted (and literal) example in ''Fanfic/GuardiansWizardsAndKungFuFighters''. During the Battle of the Meridian Plains, Viceroy Khenel's cavalry forces arrive and seem to be about to finish off the outnumbered Rebellion, only to instead turn and attack the forces of the other nobles, Khenel having defected to the Rebellion offscreen some time ago.

[[folder:Film]]

* A similar case at the beginning of ''Film/TomorrowNeverDies'', where the BigBad has the survivors of the British frigate he sank machine-gunned while they paddled up to his ship hoping for rescue.

* The Creator/JeanClaudeVanDamme film ''Second in Command'' ends this way. The Moldovan armored division that arrived to relieve the US embassy is working for the BigBad; they end up getting their asses kicked by the ''real'' cavalry in the form of [[SemperFi Marine]] [[GunshipRescue helicopters]].
* In ''Film/FightClub'', once the Narrator realizes the full extent of [[WesternTerrorists Project Mayhem]]'s plans, he goes straight to the police to tell them everything... [[ExplainExplainOhCrap only to realize the officers he's talking to are part of Fight Club.]]
* Happened in ''Film/ReadyToRumble'' when Jimmy King got betrayed by his own faction "The King's Men".

* On ''Film/{{Eraser}}'', Kruger takes part in a rescue mission to save a compromised witness but it turns out his team is dirty. The witness and her protectors are killed and he is framed for it.
* On ''Film/LastOfTheMohicans'', Colonel Munro finds out General Webb's army is at Fort Edward just two days march from him. Webb flat out refuses to help and advises surrender to the French.
* In ''Film/TheLoneRanger'', the army guy does a FaceHeelTurn after finding out he massacred innocent Indians.
-->"These men work for the railroad. So the question is... (points his gun at the Ranger) who the hell are you?"
* ''Film/SuicideSquad2016'': A helicopter arrives to extract Waller and the Squad from Midway City. However, the chopper fails to responds to hails from the Squad and then opens fire on them; having been hijacked by the Joker and his gang.
* In ''Film/TheLordOfTheRingsTheTwoTowers'', it was at first believed that this was the fate of Merry and Pippin when the Uruk-hai who had captured them were attacked by the Rohirrim army; the army leader telling Aragorn and the others they left no survivors. Fortunately, [[SherlockScan Aragorn found signs on the battlefield that Merry and Pippin managed to escape in the chaos]].
* ''Film/theMonsterClub'': In the third story, Sam manages to escape from the village of the ghouls with the aid of Luna. Luna is killed, but he manages to make it to the motorway and flag down a passing police car. The police agree to take him to the police station, only to return him to the village: revealing that they are a police escort for the Ghoul Elders returning from London.
* ''Film/NothingButTrouble'': After escaping from Judge Valkenheiser's grasp, Chris and Diane go back with an entire army of state troopers in tow to arrest the HangingJudge. It becomes obvious that they're ALL in league with Valkenheiser when they turn their weapons on the pair.
* ''Film/RevengeOfTheSith'': The 41st Elite Corps, led by Master Yoda is sent to Kashyyyk to repel [[MemeticMutation the droid attack on the Wookiees]]. But then Order 66 is issued and the clones, Gree and Jek, turn against Yoda though he beheads them before they could lay a shot into him due to the Jedi Master [[MySignificanceSenseIsTingling sensing the deaths of his fellow Jedi via the Force]]. Chewbacca and Tarfful help Yoda escape Kashyyyk, and despite the Separatist forces under General Linwodo [[LetNoCrisisGoToWaste taking advantage of Order 66 putting the Republic forces in disarray]], the Clones under Faie regrouped and defeated the droids, though most of the Wookiees are captured by the clones and enslaved by the newly-created Galactic Empire.
* ''Film/HeadlessHorseman'': While trying to escape the TownWithADarkSecret of Wormwood Ridge, the teens flag down the sheriff's cruiser. Sheriff Otis invites them in and promises to get them to safety. However, he is part of the conspiracy and goes to deliver them back to town.
* In ''Film/TwentyThousandLeaguesUnderTheSea'', after Ned and his group are shanghaied by Nemo, he sets out several messages in bottles with the coordinates of their destination: Nemo's island base of Vulcania. Upon reaching the island and seeing several warships, Ned tries to attract their attention and let them know they're friends, only for the landing parties to shoot at him, seizing Nemo's scientific discoveries their only goal.
* In ''Film/TimberFalls'', Sheryl escapes from the cabin and flees being chased by Deacon. She sees the pickup being driven by Clyde, one the park rangers, and flags him down. However, Clyde turns out to be kin to Ida and Deacon, and knocks her out.
* A variation in ''Film/WhereTheSpiesAre''. Creator/DavidNiven's character foils a KGB assassination only to be chased by the target's bodyguards. However a helicopter flies over and lowers a rope ladder for him. Once inside he congratulates British intelligence for being on the ball when [[OhCrap he suddenly realises the helicopter is flown by KGB agents]] and was meant to help the ''assassin'' get away.
* In ''Film/WildWildWest'', Not exactly in combat, but Arliss Loveless promises Bloodbath [=McGrath=] and his men assistance in reviving the cause of the Confederacy. As his men wait to meet up with their support, a tank rolls up and opens fire on them. An especially cruel example, as his only reasons seem to be testing out his new weaponry, and getting revenge on his former comrades for surrendering at the end of the Civil War.

* ''Literature/ASongOfIceAndFire'' pulls one of these, when the "reinforcements" turn out to be invaders.
** Tywin Lannister "helped" win Robert's Rebellion when his army sacked the capital instead of defending it for House Targaryen.
** Most infamously at the end of ''Literature/AGameOfThrones'' when the Goldcloaks turn against Ned Stark.
** And it happens twice in quick succession in ''Literature/AClashOfKings'', when Ser Rodrik's forces are betrayed by Ramsay Bolton's forces while they are about to launch an attack to retake Winterfell-- and then mere pages later when Ramsay the Bastard of Bolton betrays Theon Greyjoy, the man who took Winterfell in the first place, after he opened the gates to his "allies."
** During the Red Wedding in ''Literature/AStormOfSwords'', Roose Bolton and his men storm into the room. Catelyn thinks they're there to help her and Robb: however, Bolton is really in league with the Freys, cuts down his fellow northmen, and stabs Robb in the heart.
** A backstory example in ''Literature/FireAndBlood''; at the final battle of [[CivilWar the Dance of Dragons]], an army loyal to King Aegon II clashes with a rival force of his late half-sister Rhaenyra's supporters, now battling to put her son on the Iron Throne. Once both armies are locked in battle, Aegon II's commander Borros Baratheon orders his reinforcements to attack...but most of said reinforcements are former Rhaenyra loyalists fighting under duress for Aegon II, and they promptly attacked Lord Baratheon's army from the rear, exterminating Aegon II's last remaining army and leaving his enemies with a clear path to the capital city to depose him.

* In Creator/GrahamMcNeill's TabletopGame/{{Warhammer 40000}} Literature/HorusHeresy novel ''Fulgrim'', the loyalist Marines on Isstvan V do not realize that only three of the Legions going to confront Horus are loyal; their other "allies" turn on them as recounted below.
* Creator/JackChalker's ''Lilith: A Snake in the Grass'' features the sudden arrival of troops supposed to aid the witches in their attack on the protagonist's enemy, only for both defenders and cavalry to turn on the witches, the protagonist realizing he'd been an UnwittingPawn in a plan to get rid of the witches.
* In ''Franchise/StarWars'' ''Literature/LegacyOfTheForce'', series villain Jacen Solo has his fleet surrounded by Confederation vessels in orbit of Kashyyk. He is just beginning to despair when the supposedly allied Hapan armada shows up. Thinking that victory is in his grasp he contacts the Hapan Queen Mother, his lover who is in command of the fleet, to coordinate with her only to have her give him an ultimatum to surrender.
* ''Literature/IronCouncil'' in Creator/ChinaMieville's Literature/BasLagCycle, sequel to ''Literature/PerdidoStreetStation'' and ''Literature/TheScar''.
* In ''Literature/TheDresdenFiles'' book ''Changes'' has a double whammy. In the climactic scene, Martin arrives at a standoff between Susan and the Red King... only to take down Susan, revealing himself as TheMole. Except [[ThanatosGambit he does this so Susan will be able to kill him and become a vampire]], allowing Harry to wipe out the Red Court.
** Less notable but still important in the same scene was Lea disguising herself as one of Lords of the Outer Night so she could distract the vampires during the double whammy.

* Inverted during the Battle of Thull Mardu in ''Literature/TheBelgariad'', when King Drosta Lek Thunn of the Nadraks ends up clearing a path for the Western forces, betraying his fellow Angaraks, knowing that siding with the Mallorean forces would only mean subjugation, whereas siding with the West might get his fellow Angaraks' boots off of his neck.

* The Battle of Ankara between the [[UsefulNotes/TurksWithTroops Ottomans]] and [[UsefulNotes/TimurTheLame Timurids]] was a crushing defeat for the former, since a substantial force of Black Tatars deserted them on their side deserted them when they saw the odds where on their side and joined the stronger side. This battle resulted in the first and only time an Ottoman sultan was taken captive and it was followed by a {{succession crisis}} when his sons fought each other in a {{civil war}} for the throne.

* The famous [[WhamEpisode Wham Level]] of ''VideoGame/ModernWarfare2'' ends with the team holding a cabin against an endless stream of attackers while a huge amount of data is copied on a portable hard drive and most of them are dead when all of the data is secured. The last men make a frantic dash down a hillside without any real cover while under fire from lots of automatic rifles, machine guns, and rocket launchers and just 14 meters from the extraction point the player gets downed. When you regain consciousness a few seconds later, your last teammate Ghost drags you by your jacket and finally helicopters of Shadow Company appear from behind you and mow everything down with their miniguns. And when you finally stumble the last steps to the evac chopper, General Shepherd takes the hard drive and shoots both you and Ghost in the chest. The last thing you see is your bodies being thrown in a ditch, a soldier emptying a gas canister over you, and Shepherd throwing his burning cigar at your face.

* Wrestling/MattHardy running down to ringside with a chair during his brother Wrestling/{{Jeff|Hardy}}'s match with Wrestling/{{Edge}} at the 2009 Royal Rumble. This one still managed to surprise because Matt had legitimate gripes with Edge, and even if you did not know that, Edge had sent Matt packing from Monday Night Raw after stealing his girlfriend (well, Kane stole her first but we digress).