This works best with whiteboards but you can do it with paper. Split the group into multiple teams, of ideally 3 or more, and give them each a whiteboard split into two sections: shield and spear. Each round the teams will decide which player on their team to protect (shield) and which player on a different team to attack (spear). These will be revealed at the same time and you will go around and put a sticker on the forehead of anyone who was attacked, unless their team shielded them this turn. When a player has two stickers they are dead (unshielded attacks from multiple teams results in multiple stickers), when a team only has one player left they are eliminated. Keep playing until only one team is left.

Scoring is, as always, completely arbitrary, you can award only the winning team or award points on a sliding scale based on elimination. Decide how you wish based on the number of players.

Adjust the number of hits it takes to kill someone, based on the number of teams.