Free For All
Free For All, abbreviated as FFA, also known as Cutthroat and Last Standing, is the essence of Belegarth. The rules are all those contained within the Book of War, and nothing more. No teams. No boundaries. No objective. Just lay on.
A true FFA ends arbitrarily, since there is no objective and so nothing constitutes a win or loss. What to do within the rules is Free For All to choose.
Last Standing
To incite competition, Last Standing can be introduced as an objective. The closer a player gets to being the last living player, the more they've won. Most fighters probably assume this objective is always part of a Free For All.
Cutthroat
If somebody suddenly yells the word cutthroat, it has the same effect as "Last Standing, lay on!" in many fewer words. A game of Last Standing starts instantly.
Captains' Cutthroat can be used to determine captains for a battlegame.