What is your son's FB velocity at this point (before the sidearm switch)? If it's me and my son had a chance to play in college as a pitcher, I'd be very much against this change. A kid throwing sidearm is looked at as a novelty by college coaches....not as a true pitching prospect, unless he is unbelievably good. My thought is unless your son is throwing in the upper 60's or low 70's, which isn't going to get varsity guys out anyway I'd really have to consider talking to the coach....both because of the pain/soreness issues...and also the fact that it's basically taking away any chances of your son moving on beyond HS as a pitcher