1. Actually could a baseball could act as a "lifting body"?
2. But there could be a thermal updraft over home plate due to the temperature gradient difference between the grass/dirt and the reflective plate.
3. Not only that, the catch could be blowing his breath outward, causing the ball to stall over the plate.
4. It could be Ground Effect!
"When a wing is flown very close to the ground, wingtip vortices are unable to form effectively due to the obstruction of the ground.
The result is lower induced drag, which increases the speed and lift of the aircraft while it is experiencing the ground effect...
Ground effect is a major factor in aircraft "floating" down the runway, and is the reason that low-wing aircraft have a tendency to float more than the high-wing varieties...
http://en.wikipedia.org/wiki/Ground_effect_(aircraft)
Is Ground Effect the reason a Knuckleball “floats”?