I spawned two zombies: one named "Attacker" and another "Defender". I run these two commands, "execute at @e[name=Attacker] run summon snowball ~ ~2.3 ~ {Motion:[0.0,-1.0,0.0],Tags:["Snowball1"]}" then "data modify entity @e[tag=Snowball1,limit=1] Owner set from entity @e[name=Defender,limit=1] UUID", so they attack each other. As soon as Defender zombie "Throws" the snowball it starts taking random damage not from the Attacker zombie.