An excerpt from Dave Briccetti’s first non-trivial Minecraft mod, inspired by Devoxx4kids Sharp Snowballs: https://github.com/devoxx4kids/materials/tree/master/workshops/minecraft

gistfile1.scala

class SharpSnowballArray {

  @SubscribeEvent
  def replaceSnowballWithArrow(event: EntityJoinWorldEvent) {
    val entity = event.entity
    val world = entity.worldObj
    entity match {
      case snowball: EntitySnowball if ! world.isRemote =>
        -2 to 2 foreach(xOff => {
          -2 to 2 foreach (yOff => {
            world.spawnEntityInWorld(makeArrow(world, snowball, xOff, yOff))
          })
        })
        snowball.setDead()
      case _ =>
    }
  }

  private def makeArrow(world: World, snowball: EntitySnowball, xOff: Int, yOff: Int) = 
    new EntityArrow(world) {
      setLocationAndAngles(snowball.posX + xOff, snowball.posY + yOff, snowball.posZ, 0, 0)
      motionX = snowball.motionX
      motionY = snowball.motionY
      motionZ = snowball.motionZ
    }
}

Say, feel free to type in the code to make the arrow translations work no matter what the player orientation. :-)