50 means the guy tends to hit the ball back through the middle (at the pitcher). 100 means he pulls everything; 0 means he pushes everything. For a RH hitter, a 100 Pull means the 3b coach needs a helmet and the 3b/SS are going to be busy; if he's LH, 1b and 2b. For a "push" hitter (think Derek Jeter), a RH pushes the ball to the side (1b/2b/RF) more than he pulls it.
That all said, I pay no attention to it.