How to check who is the attacker when an entity is hurt? (+ player_persistant_variables)

I want to make that when any entity is attacked, it will check if the ATTACKER is a player, and with that, it will get a player_persistant_variable value from that player and do something with it. I know how to call a procedure when an Entity is attacked, but I just don't know how to check if the ATTACKER is a player