->''"Fact: The key to any successful cooperative test is trust. And as our data clearly shows, humans cannot be trusted."''
--> -- '''Cave Johnson''', ''VideoGame/{{Portal 2}}''

A Team Killer is a person who murders other people on their own team.

If you are a member of a group of people dedicated to doing dangerous work, you're probably depending on the other members of your group to back you up. You might not [[TeethClenchedTeamwork like them]], but you'll trust them at least enough not to shoot you in the back. That way, when they shoot you in the back anyhow, the betrayal just makes it all the more shocking.

Villains might do this to each other for any number of reasons, because villain team-ups are generally unstable things at best. Villainous team-killing is most often done to [[KickTheDog demonstrate]] [[ObviouslyEvil how evil someone is]]. Heroes normally don't team-kill, or at least believe that they shouldn't, because they depend on ThePowerOfFriendship to bring them through things that would destroy less unified groups.

PlayedForDrama, a Team Killer is usually a reprehensible person, who everyone despises as a traitor. Team Killing is often a MoralEventHorizon. A pre-emptive strike to stop a party member from doing something despicable is even more tragic. Occasionally Team-killing is depicted as NecessarilyEvil, but even then it's nearly always morally ambiguous at best.

PlayedForLaughs, a Team Killer is either LethallyStupid, or a {{comedic sociopath|y}} taken to its logical extreme, and chances are pretty good that the Team-Killed [[AssholeVictim deserved it]].

The term originates in online multiplayer FirstPersonShooter games, where certain adolescents take joy in deliberately killing their team-mates. "What the hell, man? Don't team-kill!" is used as an admonishment to this very day. Team killing tends to earn the ire of server admins as well, which can result in the team killer being kicked and/or banned from the server.

Incidents of it being done on purpose generally involve UnfriendlyFire. A Team-Killer who kills his own employees might be a BadBoss; see YouHaveFailedMe and YouHaveOutlivedYourUsefulness for elaboration. In large amounts, it's WeHaveReserves.

See BetrayalTropes for a list of many of the people, reasons, and methods involved in Team Killing. For when Team Killing is done in a strictly meta-videogaming sense, see {{Griefer}} or PlayerKilling.

No real-life examples, please. In real life, the matter of who's on what "team" tends to be a lot less distinct than it is in fiction.



[[folder:Anime & Manga]]
* ''Manga/{{Berserk}}'': Both Guts and Griffith.
** Guts, in a sympathetic and non-evil example, did this when he was just a kid to one of his adoptive father's men during a battle as revenge for raping him.
** Griffith's case involved [[spoiler:sacrificing his entire goddamned army to become the fifth member of the Godhand]]. [[MoralEventHorizon Slightly less sympathetic]].
** Corkus did make a few pathetic attempts on Guts's life.
* ''Manga/RaveMaster'': [[AxCrazy Lance]] kills [[EliteMooks Bis]], one of his underlings, apparently because he was taking too long to kill an enemy that Lance wanted a turn with.
* ''Anime/DragonBallZ'': Vegeta kills [[spoiler:Nappa]], his fellow Saiyan, when the latter is defeated by Goku.
** And the series started off with Piccolo pulling this on Goku, though partly because he ''had'' to to finish off Raditz. ([[ItsPersonal He still wanted to kill Goku himself.]])
* In ''Anime/SuperDimensionFortressMacross''/''Anime/{{Robotech}}'', Kamjin [[NamesToRunAwayFromReallyFast the Ally-Killer]]/[[DubNameChange Khyron the Backstabber]] earns his title not from ChronicBackstabbingDisorder, but because he tends to [[TheNeidermeyer shoot his own men]] when they run or when they're in his way. To be fair, in the two occasions shown they had it coming: the first time one of his men jumped the gun in an ambush and nearly ruined it when even Kamjin/Khyron, rightly known for [[LeeroyJenkins attacking even when unnecessary]], was waiting for the right moment (he even {{lampshade|Hanging}}d it); the second time, instead, some of his men were ''[[TooDumbToLive talking of deserting in the middle of a battle before Kamjin/Khyron]]'', who reacted by shooting one to try and get the other to fall back in line (they ran, and the chase started).
* ''[[Manga/BreakBlade Broken Blade]]'': Girghe had no issues backstabbing his own team mates for no reason whatsoever.
* ''Manga/{{Naruto}}'':
** Sasuke is a team killer.
*** Sakura genuinely cared for his well-being and always did her best to support him. And how does he repay her? [[MoralEventHorizon By trying to electrocute her, strangle her, and stab her into the face within the same five minutes.]]
*** Karin was Sasuke's teammate in Taka - until he decided that she had [[YouHaveOutlivedYourUsefulness outlived her usefulness]]. It's made even worse by the fact that she [[UngratefulBastard saved his life multiple times and helped him figure the enemy's attacks out]] mere minutes beforehand.
** [[BitchInSheepsClothing Mizuki]], the first antagonist of the series, was revealed to be this in a filler arc when it was shown that he killed his teammates during a mission for being weak.
** Kakuzu often loses his temper and kills anyone nearby, which as a member of Akatsuki, usually resulted in him killing his partner. Eventually, he was paired with Hidan because even if [[TeethClenchedTeamwork they hated one another]], Kakuzu wouldn't be able to kill him.
** Kisame did this to a group of code-breakers from the Mist village to prevent them from falling into the enemy's hands. When he gets teamed up with Itachi, he makes note of how they both massacred their comrades.
** Pre-HeelFaceTurn Gaara makes death threats against his teammates (who happen to be his older brother and sister) when they object to taking unnecessary risks in the Forest of Death.
* Comes up a ''lot'' in ''Manga/{{Bleach}}'' among the villains. Grimmjow Jaegerjaquez lost his rank when he lost his arm (that held his rank tattoo) and was replaced by [[spoiler:Luppi Antenor]]. Grimmjow came back and the two fought over the rank, with only one surviving. Zommari Rureaux and Nnoitra Gilga did this to their fellow espada. Rudbornn Chelute was an arrancar whose ''job'' was to slay defeated arrancar. And Giselle Gewelle did this to [[spoiler:her former boss]].
** Pepe Waccabrada [[InvokedTrope tried]] to do this to Liltotto Lamperd with a [[BrainwashedAndCrazy brainwashed]] [[SuperStrength Meninas McAllon]] [[ForTheEvulz just because]]. [[spoiler:Unfortunately for him, [[ImAHumanitarian Liltotto]] survived and [[KickTheSonOfABitch paid him back in kind.]]]]
* In ''Manga/YuYuHakusho'', Seiryu does this to Byakko

[[folder:Comic Books]]
* ''ComicBook/{{Invincible}}'': This is how we find out that Omniman is not quite the hero that everyone thinks he is.

[[folder:Films -- Live-Action]]
* ''Film/{{Aliens}}'': Burke attempts to have Ripley and Newt impregnated by a facehugger in order to smuggle alien embryos back with him, which would render them ticking time bombs. Thankfully, he fails.
* In ''Film/GuardiansOfTheGalaxy'', Ronan kills The Other for lecturing him on showing respect in Thanos's presence.
* In ''Film/HornetsNest'', IgnoredExpert Captain von Hecht shoots SS officer Taussig after a heated spat that ends with Taussig refusing to acknowledge the danger the dam is in. He then lies to Taussig's MookLieutenant and says "The shock of the incident was [[DrivenToSuicide too much]] for the Major."
* In ''Film/TheBridgeAtRemagen'', Major Kreuger shoots two of his men who try to run away. [[spoiler:He's later executed himself by the SS.]]
* All of the Joker's team at the beginning of ''Film/TheDarkKnight''.
* In ''[[Film/TheDirtyDozen The Dirty Dozen: Next Mission]]'', there's a very bizarre scene on the train wherein General Dietrich shoots his aide Schmidt. [[spoiler:Apparently Schmidt was beginning to suspect Dietrich intended to assassinate Hitler, and Dietrich shoots him to keep him quiet, but this is never explicitly stated.]]
* ThoseWackyNazis sure do love doing this. SS Major Kaempffer blows Captain Woermann away in the film version of ''Film/TheKeep''. [[spoiler:They'd just had a heated argument, and then heard gunshots outside. Although never explicitly made clear, Kaempffer had apparently been looking for an excuse to kill Woermann for constantly criticizing him. As a bonus, he also seemingly did it to steal Weormann's cross in a doomed effort to protect himself from Molasar.]]
* [[spoiler: Cypher]] in ''Film/TheMatrix'', after becoming disgruntled with life in the Real World and making a deal with the Agents to re-insert him into the Matrix.

* Literature/TheBible: Judas is so infamous that his name is now a synonym for "backstabbing traitor." He's the inspiration for the FindingJudas trope.
* ''Literature/GauntsGhosts'': Lijah Cuu [[spoiler:kills troopers Bragg and Meryl and tries to murder Saint Sabbatine herself before being brought down... but not before killing fan favourite ColonelBadass Colm Corbec in the crossfire.]]

[[folder:Live-Action TV]]
* One of the ongoing subplots in ''Series/{{Firefly}}'' is Jayne's willingness to sell out TheTeam, specifically River and Simon. The subplot is resolved when [[spoiler:Mal finds out about Jayne's attempt to turn in the Tams to the Feds on Ariel and almost [[ThrownOutTheAirlock throws Jayne out the airlock as the ship is taking off for it.]]]]
* ''Series/{{Battlestar Galactica|2003}}'': Tragically and repeatedly due to Cylon infiltrators.
* On ''Series/{{NCIS}}'', poor [[spoiler:Special Agent Lee]], a rare semi-sympathetic version, was forced to kill [[spoiler:Langer]] after [[IHaveYourWife a loved one was kidnapped.]]
* The previous leader of Series/{{Torchwood}} Three [[MurderSuicide killed his entire team and then himself]], leaving Jack Harkness to rebuild the team.
* In ''Series/PowerRangersNinjaStorm'', Vexacus kills both Zurgane and Motodrone as part of his plan to seize control of Lothor's ship.
* In ''Series/{{LALaw}}'', Stuart is so upset on how another paintball player is cheating -- he's continuing to play after he was shot and had to forfeit his chip -- that Stuart begins shooting him multiple times. Brackman tells Stuart, who is one of his teammates, to knock it off -- he's proven his point -- but Stuart keeps shooting the guy, so finally Brackman shoots Stuart, then says, "Give me your chip."
* Bringing a bunch of magically gifted teenage girls together is going to cause this at best, but the most obvious example from ''Series/AmericanHorrorStoryCoven'' is [[spoiler:Fiona Goode, the Supreme Witch of the Coven]]. The first instance is because [[spoiler:she thought Madison was the next Supreme, so Fiona killed her in order to prevent Madison replacing her and draining her powers/life force. She later kills Nan in a deal with Papa Legba.]] This isn't the first time, as [[spoiler:Myrtle rightly believes that Fiona killed the Supreme of the last generation as well in the same manner, as she killed Madison but was unable to do so.]]

[[folder:Tabletop Games]]
%%* {{Munchkin}}s do this to steal exp and items.
* Most factions in ''TabletopGame/Warhammer40000'' do at least a little bit of Team Killing. The Orks and Chaos in particular have built societies on it. Specific characters known for being Team Killers include:
** [[NamesToRunAwayFromReallyFast Kharn the Betrayer]] earned his name this way on Skalathrax. When night fell, the sub-subzero cold caused both sides to stop fighting and look for shelter. Kharn took offense at this lack of moral fiber and ran around setting the shelters on fire, regardless of who was in them. Through this act, Kharn singlehandedly destroyed both the World Eaters' and the Emperor's Children ability to function as a unified force (limiting them to mercenary work or small warbands), was chosen as Khorne's immortal champion, and was given the fanon reputation of a PsychopathicManchild who sticks melta bombs on troop transports for fun.
*** He never stopped, either. His model's rules state that he will hit any enemy in melee combat on a die roll of 2+; if he's going solo he'll just miss the enemy on a roll of 1, but if he's in a unit at the time [[UnfriendlyFire any rolls of 1 will be allocated to friendly models instead]].
** [[ThePoliticalOfficer Commissars]] are supposed to kill the men in their company if they try to run away during a fight or somehow violate protocol, but the most rabid ones just kill willy-nilly for any reason they like.
** Literature/{{Horus|Heresy}} is worse than standard team kills because this team was his ''family''.
** In Warhammer Fantasy Battles, the Skaven had this as one of their hats. They alone could target units with ranged weapons without caring if they hit their own forces. Given that Skaven CanonFodder were so cheap in points that WeHaveReserves kicks in, a Skaven player should think nothing of trading off a few of their chaff units in exchange for hitting the enemy as well.
* [[Blog/ThingsMrWelchIsNoLongerAllowedToDoInAnRPG Mr. Welch]] has occasionally forged [[WeaponOfXSlaying Weapons Of X Slaying]] to take out particularly annoying party members.
* In ''TabletopGame/{{Paranoia}}'', ''everyone'' is expected to be this, and the game specifically tempts them with motives and opportunities aplenty.

[[folder:Video Games]]
* Pick any team-based multiplayer game where FriendlyFireproof is not enabled. {{Griefer}}s are often [[PlayerKilling team-killers.]]
** In ''VideoGame/WorldOfWarcraft'', it's possible to use certain encounter mechanics to kill your fellow party members (for example, standing next to someone with a debuff that harms everyone nearby). Most people do this by accident, but the potential for deliberately killing someone exists.
** [[https://m.youtube.com/watch?v=JoDLZhZZOIw One video]] showed a ''VideoGame/TeamFortress2'' server that briefly deactivated FriendlyFireproof. The second the players realized what had happened, they began shooting their teammates.
** Friendly Fire can be very powerful at higher difficulties in ''VideoGame/Left4Dead2'', so it's a very popular tactic for griefers. Fortunately, it's just as easy to work together to keep the griefer dead until they RageQuit (Though you'll be down a man, and with only four survivors that's quite significant on its own). Friendly fire does full damage at the highest difficulties, but is reduced on lower difficulties. On easy, [[FriendlyFireproof most weapons do no damage to teammates]], with only [[MolotovCocktail molotovs]], [[ExplosiveBarrel gas cans, and propane tanks]] remaining an option for would-be team killers.
** In ''Videogame/{{Planetside}} 2'', team-killing will result in warnings and eventually your weapons being locked down. The New Conglomerate faction has a reputation for team-killing, largely because their weapons are high-damage and slow-firing, so NC troops firing wildly and accidentally hitting their allies can kill them near-instantly.
*** This gets to be a problem with [[InstantDeathRadius MANA Turrets and MAX suits]] used to lay down suppressing fire on a corridor, generally one of the better ways to hold off an attack. Then you get [[TooDumbToLive Light assaults barging into the 10-lane bullet highway]]. ''[[DeathIsCheap Repeatedly]]''. Then the bullet-hose keeping the enemy off you is shut down for teamkilling and you lose.
* Many traditional RPG's such as ''Franchise/FinalFantasy'' allows you to KO your own team members, and many are willing to do so for reasons such as protagonist-based LevelScaling, CantDropTheHero, and TheScrappy that pointlessly reduces EXP rewards. In certain ''Final Fantasy'' games, certain moves or abilities will only work if other people in the party are knocked out. This can lead to players intentionally attacking their own team just to get the effects they were seeking.
* It's a common element in the ''Franchise/{{Disgaea}}'' games that killing too many of your own units, intentionally or not, often locks you out of the better endings.
* ''[[VideoGame/DissidiaFinalFantasy Dissidia 012]]'' has [[spoiler:[[VideoGame/FinalFantasyIV Kain]]]] playing the WellIntentionedExtremist variant of this. He also convinces [[spoiler:[[VideoGame/FinalFantasyI Warrior of Light]]]] to join in on the plan, and they're both [[WhatTheHellHero chewed out quite extensively]] by [[VideoGame/FinalFantasyXIII Lightning]] when the betrayal is revealed. [[spoiler:Kain]] has ''really'' good reasons for doing so, however; [[spoiler:[[VideoGame/FinalFantasyIV Golbez]] tipped him off that if the [[HumanoidAbomination manikins]] defeat any of the warriors during the war, they'll be KilledOffForReal, as the gods will not be able to revive them. This is why the likes of Lightning, Kain, [[VideoGame/FinalFantasyXII Vaan]], [[VideoGame/FinalFantasyVIII Laguna]], [[VideoGame/FinalFantasyVII Tifa]], and [[VideoGame/FinalFantasyX Yuna]] are not present in the first game; [[HeroicSacrifice they died ensuring that the Rift would be closed, preventing a huge influx of manikins into the cycle of war]].]]
* In ''VideoGame/BaldursGate'', if you recruit Minsc, Dynaheir, and [[ArchEnemy Edwin]], the former two and the latter will eventually go at it.
* There are several points in ''VideoGame/DragonAgeOrigins'' where you can kill party members (or party members can kill you) as a consequence of "ethical disagreements".
* The same can happen in another Bioware production, ''Franchise/MassEffect'', the most glaring potential examples being [[spoiler:Samara]] in the second game: you can kill her off just like that and employ [[spoiler:her murderous daughter]] to fulfill the same role on the team. There is no substantial loss nor gain from doing so.
* In ''VideoGame/JadeEmpire'', the player character can do this to about half of his/her party.
* In ''VideoGame/MetroidOtherM'', there is a mysterious character known as the Deleter. It is clad in armor identical to that of the Galactic Federation soldiers Samus works with over the course of the story and was sent with the 07th Platoon to kill all witnesses to prevent them from discovering the links between the Bottle Ship and the Federation. While the subplot is dropped before being fully solved, it's heavily implied that the person in question is [[spoiler:James Pierce, the communications expert of the squad.]]
* In ''VideoGame/NieR'', [[spoiler:the final ending provides you with the choice: either kill Kainé, putting her out of her misery, or give up your own life to get rid of the Shade possessing her.]]
* In ''VideoGame/UltimaV'', Saduj is a joinable NPC who will attack your other party members the minute you enter combat with him in the party. This pretty much serves you right, not only is he an open supporter of King Blackthorn whom your party is actively working to overthrow, but [[SdrawkcabName his name is clearly "Judas" spelled backwards]].
* The ''Videogame/{{Portal 2}}'' quote atop the page comes from a preview trailer for the game, where one stick figure pushes another into a fire for no reason. The solution: robots! After rigorous trust exercises, robots are able to work together for an impressive ''six seconds longer''. In-game, there are several co-op achievements that involve deliberately murdering your partner.
* In ''Septerracore'' putting certain combinations of characters in your party is ill-advised, as they ''will'' occasionally swipe at each other for real damage.
* In TheEndTimesVermintide, the enemy Skaven have no compunctions about hitting their allies with AOE effects if the players are also threatened by the attack. This was a trait of the Skaven from the Table Top Game Warhammer.
* The ''VideoGames/{{Halo}}'' games' MultiPlayer allows players on the same team to kill each other, though doing it enough times will result in the offender being kicked out for poor sportsmanship.

[[folder:Web Animation]]
* ''Machinima/RedVsBlue'':
** Caboose accidentally killing Church is something of a running gag. Whenever they want Caboose to kill somebody, they just tell him to "help" the enemy. He has the largest body count of the Blue and Red Teams and ''all of them are team kills''. He nearly depopulated a Blue Army base off-screen. Command ''even has a keyboard shortcut'' for recording Caboose's team kills: [[StealthPun Ctrl+F+U.]]
** Caboose accidentally killing Church (the first time)? ''[[TimeyWimeyBall Church's fault]]''. Granted, it was Gamma who tortured Alpha with simulations in the past, so it could have been Gary/Gamma simply screwing with him.
--->'''Church:''' Oh, my god. ''I'm'' the team-killing fucktard!
** Sarge will take every opportunity to kill Grif.

[[folder:Web Comics]]
* ''Webcomic/EightBitTheater'' has Black Mage. Sometimes Red Mage or Thief, but mostly Black Mage.
* Referenced in ''Webcomic/PennyArcade'', when [[ItMakesSenseInContext the Twelve Apostles are playing]] ''Franchise/{{Halo}}''.
-->'''Peter:''' Christ, Judas is team killing again.\\
'''Christ:''' Judas, don't be a dick.
* Yeon from ''Webcomic/TowerOfGod'' is a fire mage that regularly fries her own team members by accident, among them Ja Wangnan, the main character whose life is in danger because he keeps failing the tests. When they meet yet again, HilarityEnsues.
* There's no ''fatalities'' in ''Webcomic/TheOrderOfTheStick'', but [[TriggerHappy Vaarsuvius]] and [[HeroicComedicSociopath Belkar]] have come close on occasion.
-->'''Roy:''' Dammit, Vaarsuvius, I've told you before, we do NOT blow up members of our party!\\\
'''Roy:''' ''[to Belkar]'' If you kill Elan for [=XP=], we'll kill ''you'' for [=XP=].

[[folder:Web Original ]]
* Vegeta (unsurprisingly - see above) in ''LetsPlay/TwoSaiyansPlay''. He's especially trigger-happy when he and Nappa play ''VideoGame/{{Magicka}}'', and indulges in the EvilLaugh while doing so.
* ''Series/{{Noob}}'' has shown this a couple of times:
** In Season 4, [[spoiler:Gaea ends up factionless in presence of her guild and a couple of fanboys of hers from the enemy faction. Her FaceHeelTurn happens via her getting her fanboys to form a PickUpGroup with her and killing her guildmates to get reputation with her new faction]].
** In Season 5, Roxana doesn't let a bunch of members of her faction stand in the way of a chance to deal decent damage to the game's BigBad.
** According to the novels, this is how Lorth Kordigän ended up being Helkazard's successor. Intially, Helkazard was being replaced by a ''council'' of which Lorth Kordigän was member among many.
* ''Roleplay/TrespassersOfTheMultiverseGaiden'': Bisnif. His very skills are geared for this, and he outright attacks his own teammates and puts them at risk.

[[folder:Western Animation]]
* ''WesternAnimation/TotalDrama'':
** Courtney becomes one in ''World Tour'' in order to get a chance to vote off Gwen.
** Scott is a characteristic example in ''Revenge of the Island''. He seems more interested in eliminating his own teammates than the other team, wanting to lull the other team into a false sense of security so they will eventually be easier to pick off. He's sneaky enough that he can pull this off without getting booted. As of ''All Stars'', he drops the act and starts playing fair, presumably because he knows that such a strategy wouldn't work twice.