Introduction letter question...

IMO you are in the same boat as a lot of HS juniors, many who last year played JV and are just getting their shot at varsity. Intro letters are just expressing interest in a program. No need to mention an injury there. It may come up eventually, but as long as he is fully recovered and throwing well, he will be judged on how he currently performs.

My son had an injury his sophomore year that prevented him from pitching and limited him to just being a DH. In the first contact letters he also included a bio page and his current HS schedule when available. He didn't mention stats initially (since he really didn't have any), and only updated the bio page as he developed relevant varsity stats his junior and senior years. Then for the sophomore year under pitching he put DNP. Very few, if any people actually questioned it. And if they did, he told them about his injury.

He still received responses and actually ended up at one of the schools he originally contacted during the fall of his junior year.

I think birdman gave good advice. Just advise your son to introduce himself, include a schedule (HS and summer), a transcript and in each letter, specifically (and personally) tell them why he's writing to them.

They don't care much about the stats anyways. They will just want to know where they will see him.

They don't want stats at all!