Hit-f/x puzzle

The following plot was made using the hit-f/x data recently made available by SportVision. Plotted along the horizontal axis is speed of the ball off the bat (in mph). The vertical axis shows the launch angle (or vertical angle): i.e. the angle of the batted ball relative to the ground.



I must confess, I don't understand the features of this graphic. Specifically, I don't understand why there are plenty of slow ground balls (speed <> 0 degrees). Maybe because of the geometry of the ball-bat collision and the non-horizontal bat angle, balls hit in the air at low speeds go foul? (Foul balls, unless they are caught for an out, are not included in the hit-f/x batted ball data.)