The ball is made by injecting a single glob of hot plastic into a mold. The mold is closed and rotated to spread the plastic evenly around the walls of the mold. When the mold has stopped spinning it is opened and the new ball is removed from the mold. Sometimes there is a minor separation seam from excess plastic that leaked out of the mold. This excess plastic is sanded off. Look inside the ball and you will not see a seam.