Minecraft wiki entry for Player_versus_Player, associated text: Cram dispensers in the walls of a tight hallway, load them with damage potions, lead a rapid clicker to them, place a switch to restrain it, and then put sticky pistons in the walls to trap people in separate rooms. Nothing, not even Heavy weapon dudes with so much as Protection X (not that that enchantment is available without editing the NBT file) can survive. One may also unleash monsters in there once the opponent is in, or use other armor penetrating methods. A clock circuit leading to pistons can render the trap unable to break out without explosions or maybe tons of liquids, if your team has really great redstone scientists, these can also be set up.