To produce a line drive that has backspin on it, the barrel of the bat must not work from under the ball, it must work through the ball. A severe upward swing will produse a topspin (ground-balls), or backspin with too steep of a trajectory into the air (pop-ups). There is very small room for error in terms of quality contact with this approach. Do we really want to tell our players to try to have an upper-cut swing? Doesn't the swing flatten out on its own when quality contact is made out front?