Snowball damage

Hi. I can not get the attacker from the player who attacks with snowballs.
I need each snowball to deal damage in 5 hp and 4 snowballs to kill the player being attacked.
Whats wrong?
public function onDamage(EntityDamageEvent $event)
{
$player = $event->getEntity();
if($player->getLevel() == $this->getServer()->getLevelByName('4b'))
{
if($event->getCause() == EntityDamageEvent::CAUSE_PROJECTILE)
{
$event->setDamage(5);
}
if ($event instanceof EntityDamageByEntityEvent)
{
$damager = $event->getDamager();
if(!isset($this->FBStatus[$player->getName()]))
{
if($player instanceof Player and $event->getCause() == EntityDamageEvent::CAUSE_PROJECTILE and round($event->getFinalDamage()) >= $player->getHealth() or $damager->getInventory()->getItemInHand()->getId() == 294 )
{
$player->setHealth(20);
$this->FBStatus[$player->getName()] = 0;
$player->hidePlayer($player);
$event->setCancelled(true);
$player->sendTitle(TextFormat::RED.'УБИТ');
$damager->sendTitle(TextFormat::RED.'KILL', '+50$');
$this->FBMoney[$damager->getName()] += 50;
$this->economy->addMoney($damager, 50);