Betrayal

Were you looking for Two Betrayals, the eighth level in Halo: Combat Evolved? In Halo multiplayer terminology, a Betrayal occurs when a player kills one of their own teammates during a team match. The act of deliberately betraying one or more teammates is referred to as teamkilling.

Background
In order for a betrayal to occur, the betraying player must be completely responsible for the death of his or her teammate. Enemy players must play little or no role in the act. For example, if two players on opposing teams are battling each other, and a third player accidentally kills his already-damaged teammate with a grenade, it will not be counted as a betrayal, and the enemy will be credited with the kill. On the other hand, gunning down a teammate in your own base while no enemies are around absolutely counts as a betrayal.

Most betrayals occur with the use of explosives, as a result of unanticipated splash damage. Almost all betrayals occurring without splash damage are deliberate, though there are exceptions -- for example, a player may betray a teammate if, while taking a Warthog over a Man Cannon on Halo 3's map Valhalla, they land on their teammate. Also, in the reverse sense, a player may be driving around in a Warthog and have a friendly player fall from the man cannon on top of them, giving them a betrayal by splatter.

In Halo 2, deliberate teamkillers are a great hassle to deal with, as such an offense was not ban-worthy. In Halo 3, a new option called "Betrayal Booting" was introduced; players that commit too many betrayals can be booted by their most recent victim even during matchmade games, with the teamkiller also receiving an EXP penalty. In Custom Games, "Betrayal Booting" can be set manually, to decide how many betrayals must occur before the player is booted. In most Matchmaking games, the betrayal count is set to two.

There are instances where a player is betrayed, is unable to boot the betrayer, and then gets booted when the retaliate against the griefer. It's unknown why this occurs.