Combat or other dangerous elements in a setting or plot conflict increase the drama by exponentially increasing the danger to the characters. But sometimes that danger comes from an unexpected angle. You look up to see who is on the other end of the knife you've just been stabbed with... and it's your best friend!?! This sort of thing can occur by accident, by treachery, or, perhaps most tragically, because they had to.
In Real Life, friendly fire usually occurs as a case of mistaken identity: innocent civilians, allies, or neutral forces, are mistaken for enemy forces and fired upon, or else the attacker simply didn't know the friendly unit was in the line of fire. While it might be hard enough to imagine the horror of killing someone you like accidentally, in fiction, to play the drama up even more, the attacker often is all too aware of what they are doing.
Given the tropes themselves tend to be fairly broad, there may be some overlap in a given situation depending on the perspective. For instance, even if the person pulling the trigger makes a genuine mistake, they might have been manipulated into doing so by a third party deliberately seeking to cause harm.
Note: Please place non - trope examples in the subtropes listed rather than listing them here.
There are many forms of Friendly Fire, from nastiest to least nasty:
Category A: Deliberately, out of a callous disregard for life (note: doing any of these invariably marks you as a villain or Anti-Hero):
- Bad Boss: mistreats his own minions for trivial reasons.
- Disposable Intern: The intern is so unimportant killing them doesn't matter.
- Kick the Dog: commit an unnecessary evil act to show the audience you're not nice.
- We Have Reserves: callously place minions in a situation where they will be slaughtered, as part of a strategy.
Category B: Deliberately, out of treachery:
- Cavalry Betrayal: The Cavalry that you've been praying for isn't really on your side.
- The Dog Bites Back: A minion takes his revenge after being the subject of too many Kick the Dog moments.
- Forced Friendly Fire: A character gains control of their opponent's firearm and forces them to shoot it at allies
- Please Shoot the Messenger: A letter instructs the recipient to kill the man who delivered it. The sender, the messenger, and the recipient are supposedly on the same side.
- Shoot the Dangerous Minion: A villain offs his henchman out of fear that the henchman will betray him.
- The Starscream: A mook who serves the Big Bad but intends to overthrow him.
- Unfriendly Fire: A murder disguised as a combat death (Fragging, see also Team Killer).
- Uriah Gambit: A Bad Boss attempts to get an underling killed by proxy by sending them on a Suicide Mission or any situation where their death will appear accidental.
Category C: Deliberately, due to being faced with a choice between evils:
- Dying as Yourself: The way to cure a victim of The Corruption is to mortally wound them, resulting in an Obi-Wan Moment.
- Kill Us Both: To stop an enemy for good, you've got to ask your friends to do this.
- Mercy Kill: To kill someone quickly who would otherwise face a painful or ignoble death.
- I Cannot Self-Terminate: Someone wants to die, but doesn't have the means to off themselves, so the hero has to do it for them.
- Sadistic Choice: A villain gives a hero a choice between letting one of two people die.
- Shoot the Dog: To prevent a more innocent or pure hero from having to kill someone, another hero does it.
- Shoot the Hostage: To stop an enemy, one must risk harming a hostage used as a Human Shield.
- Trial by Friendly Fire: Someone must act quickly to stop a threat and the solution requires putting your allies in the line of fire.
Category D: Due to an error in judgement
- Friend or Foe: Mistaking an ally for an enemy. This is Truth in Television on the battlefield.
- He's a Friend: Mutual allies of the Hero come to blows before realizing their relationship, forcing the Hero to make them both back down.
- Kick the Morality Pet: Go too far and hurt an ally, prompting a Heel Realization.
- Let's You and Him Fight: The author decides to set up a situation in a crossover to make the heroes battle each other.
- My God, What Have I Done?: A realization that good intentions have caused great harm.
- Self Offense: A character attacks an unknown potential assailant out of fear, anxiety, or paranoia, then discovers they've hurt an ally by mistake.
Category E: Completely unintentional
- Cartwright Curse: A character's love interests have a high mortality rate, through no fault of their own.
- Friendly Target: By choosing to face an enemy, a character places his friends in danger.
- I Just Shot Marvin in the Face: Mishandling a weapon and forgetting about gun safety.
- Stray Shots Strike Nothing: Although the trope itself is about missed shots being insignificant, notable aversions (the only examples listed) often involve the consequences of firing blindly and causing collateral damage.