Bukkit detectan el bloque que ahora golpeó
public void onProjectileHit(ProjectileHitEvent event) {
Entity entity = event.getEntity();
if (entity instanceof Snowball) {
Location loc = entity.getLocation();
Vector vec = entity.getVelocity();
Location loc2 = new Location(loc.getWorld(), loc.getX()+vec.getX(), loc.getY()+vec.getY(), loc.getZ()+vec.getZ());
System.out.println(loc2.getBlock().getTypeId());
if (loc2.getBlock().getTypeId()==Block.SNOW_BLOCK.id)
{
...
Jealous Jackal