Eightball

Eightball is somewhat like the reverse of a Kill the Monarch battle. Rather than having a monarch who must be defended at all costs, each team has an eightball who must be the last person on their team to die, or the other team loses.

Fighters: 4+. Above 30 or so may require rule variants, see below.
Field: any of sufficient size.
Regen: none during a battle.
Teams: Two of equal size and strength. For more, see variants below.
Rules: Each team chooses one member to be the eightball, and announces their choice to the other team. The two teams fight as normal (see field battle), but if the eightball on either team is killed when any other members of their team are still alive, their team wins. If there is a question as to whether there is anyone other than the eightball left alive on one team, a marshall should call for all living people on that team to announce themselves - any who do not may be called dead. If the eightball kills themselves or is killed by a teammate, their team loses. Depending on sportsmanship, each eightball may require a dedicated marshall to watch for hits.
Tactics: The eightball can be used offensively, by charging wildly into the enemy hoping to cause chaos, kill opponents who can't retaliate, or be accidentally killed by a careless foe. They can also act defensively, providing relief to a beleaguered side by forcing the opponent to withdraw or fight more carefully and defensively. They can also act to relieve an attack by the other team's eightball. Non-eightball fighters will find that it is best to approach the eightball as cautiously as possible and without too many fighters, to avoid an accidental death by two limb hits. Stabbing weapons, particularly spears, are invaluable for being able to gimp the enemy eightball from a safe distance while not endangering their life as much. Gimp and go is vital.
Variants: Eightballs may be denied armor. While this makes them easier to kill, it also makes their hit-status much more readily discernable and makes them more vulnerable to limb-stabs, which make the game last longer.
Eightball may become impractical with a large number of fighters, as either an eightball will die too quickly or the eightballs will be quickly gimped and the game will proceed as a normal field battle. One potential solution to this would be to field more than two teams. Rather than having the team whose eightball dies win, the team of the eightball's killer would lose, leaving the remaining teams to fight it out. Alternatively, each team could have multiple eightballs, clearly marked by a uniform tabard, headband, etc. Killing one eightball before everyone on their team was dead would not end the battle, unless it was also the last eightball on the team.