Minecraft wiki entry for Player_versus_Player, associated text: Potions harm and distort the enemy, making them the most effective against especially such people with Protection IV armor. There is no magical protection in vanilla, so armor points are useless. Snowballs and eggs will knock the enemy back. You can project them into lava or a pit, and as part of a bug in the game, it damages armor as well because it technically harms the player pummeled by it. Always try to find a way around normality!