Please Note: Even though most machines pitch leather baseballs, it is rarely beneficial to use leather baseballs in pitching machines. The internal components of a leather baseballs consists of string, glued around some type of core.
The compressing action of pitching machine breaks this adhesive, thereby softening the ball.
Pitching leather baseballs through pitching machines will dramatically reduce their useful life.
Additionally, the abrasive seams on leather baseballs will deteriorate the wheel laminate in the pitching machine much faster than dimpled balls will.
This will require a more frequent replacement of pitching machine wheels.