Is he still friends with some of his team mates?
The loss of being part of a team or his team, might be a part of the issue.

If he is physically up to it, I'd suggest he go watch some of the other sports listed that are less contact prone.
You are often still on a team, but the events/competitions are less risky, one on one or timed.
Even archery, bowling, target shooting...
might need to search up a list of teams/clubs in your city and see what appeals/fits..