Bumping this back up in case anyone has any pointers for avoiding reinjury upon return to hitting, running, lifting.
So coming from an athletic trainer's perspective, the person who has a history of 'X' injury has an increased risk of that injury again, compared to someone who has never had it. That doesn't mean it'll happen, necessarily, it just means if we are comparing two people of the same age/playing level so on and so forth, the person who has a history of whatever injury has an increased likelihood of it happening again, usually.
The best advice would be when starting up after a break (say hitting and throwing), don't do too much too soon. A way to possibly monitor that would be asking "On a scale of 1-10, 1 being super easy and 10 being you're completely gassed, how hard was that training session for you?" and then maybe being more specific if they are a pitcher too or whatever.
So you could track that in a spreadsheet and say it should be an easy training session and they're saying "I feel like that was an 8/10" then maybe that means they need an extra day of recovery, or maybe they haven't been sleeping well and that is affecting their recovery. There's no correct answer to this per se, but this could be an option.
With training, lifting, running, they should be following some sort of program, and that program should have some sort of autoregulation in it. Hey I want you to do 3x8-12 reps with a couple reps in reserve. Well some days that might be 100 pounds, some days that might be 90 pounds (as an arbitrary example).
My biggest question is how to safely get back to training while avoiding the same injury?
His training should involve getting back to the activities required of him. They can play around with many different training factors. ROM, reps, sets, weights, tempo, but if we just shield someone from hitting and throwing and the lifting they'll do in their training, and then say, "Okay well you feel better now so I guess you can go off and do the thing," then that's not the best way to set up someone for success. Doesn't mean it can't work, just, it's not the best way to go about it.
So a conversation to be had could be "What is the next step to make sure we can get back to training safely? What are some things to look out for?"