player1 picks a weapon. player2 gets nothing. game starts, and for arbitrary amount of time, player1 tries to deal as much damage as possible to player2.

player1 score = shots hit
player2 score = shots missed

player2 gets same weapon as player1. player2 gets same amount of time to deal damage.

player2 score = shots hit
player1 score = shots missed

rinse & repeat.