Wait until next time he does it and then talk to him first in no uncertain terms. Make sure you know exactly what you want to say beforhand, make sure you have thought it through, then let him have it.
Worry about the baseball bat later. See how he takes a bit of his own medicine first. His behaviour is totally unacceptable.
Make sure there are other people (i.e. your mom, and possibly a friend or two) around when you do this in case it comes to blows. That way you will have witnesses who will back you up.