You are more right than you know: Not only pitching, but hitting, too!
Deadlifts are a great way to work the posterior chain and get very heavy forearm work. Bench pressing helps you to get isometric strength there too while you push on a heavy object, which is always a nice thing to learn how to do.
Chin-Ups / Pull-Ups help too, and good old heavy bar static holds are great as well.
Oh: And taking lots of batting practice.