I am currently attempting to make snowman act hostile toward players in a multiplayer adventure map. As of now, I have a silent, invisible silverfish mounted atop each players head, which gives the snowmen something to shoot at. At each player, I test for a snowball within a radius of 2 blocks; which then triggers a command that causes players to take damage. However, when damage is dealt on one player, it is also dealt on all other players in the game.
First, I summoned a silverfish at each player in the game. From there, I teleported the silverfish to the nearest player, and then teleported it up 2 blocks. It may not be a very efficient method, but it works for what I need.
command to teleport silverfish to player (repeating command)
execute @a ~ ~ ~ /tp @e[tag=target,c=1] @p
command to teleport silverfish up (repeating command)