import crafttweaker.event.PlayerAttackEntityEvent;
import crafttweaker.event.IEventCancelable;
import crafttweaker.entity.IEntity;
import crafttweaker.player.IPlayer;
import crafttweaker.item.IItemStack;
import crafttweaker.entity.IEntityLivingBase;

events.onPlayerAttackEntity(function(event as PlayerAttackEntityEvent){
    var entity as IEntity = event.target;
        var player as IPlayer = event.player;
    if(!isNull(entity.definition)){
                if(!isNull(player.mainHandHeldItem)){
            event.cancel();
                }
        }
});