Get the real player damager behind an entity, for example if an entity was damaged by an arrow.

[Bukkit] PlayerDamager.java

public static Player getPlayerDamager(Entity damager) {
	if (damager instanceof Player) return (Player) damager;
	if (damager instanceof Projectile) {
		Projectile projectile = (Projectile) damager;
		Object shooter = projectile.getShooter(); // Doesn't really matter but will also make it work with pre 1.7
		if (shooter != null && (shooter instanceof Player)) return (Player) shooter;
	}

	return null;
}