if it was my car, i'd incapacitate the guy first by any means possible. i'd try not to send him to the hospital, but breaking his nose is fair game. then i'd call the police. if someone is delibrately attacking your property, you should be allowed to defend it. i don't know if this is really written into the law, but i seriously doubt the police or DA would have much of a case against you. now if there's no witnesses, that's another story. but i'm guessing that in this case, since it's right after baseball practice, there will be a few people around.

if it's just a PSP, i would hope to be thinking clearly enough not to overreact. i'd try to warn the idiot, and tell him "hey, give it back or i'll break your nose." and if he doesn't comply, break his nose. it's still your property. regardless of if he's deliberately damaging it, he still doesn't have a right to snatch it from you and mess with it without your permission.