Do you want it to be unlimited or drop after thrown?
mmk oh and i found a picture of a rock that i like
I made a "throwable stone" from events in Badspot's server once to break the top of an ice-covered lake on his terrain build. The next day I found he'd reset the map and there were at least ten other "ice lakes" around the place.
Maybe it could stun you a bit, less then the baseball, and probably some new sound, and it would be pretty cool.
Finished the rock. Testing it now...