When Happy is in the batting cage getting hit in the head and chest with baseballs, Chubbs pulls the plug on the machine to get him to stop. They then start chatting, and the kid who was watching gets in the cage, deposits a coin, and the machine starts spitting out balls. But it was never plugged back in!
Not only is there this mistake, but also after the boy gets hit with the first ball no other balls come out. Most batting cages make you pay like 50 cents for like five balls or something. Why would only one come out?
Maybe, just maybe, it usually ran on a plug but it also had a backup generator.
Then it would have stopped Happy's game, and restarted in time for the kid's.