Having a son who's a rugby player myself, I think it's quite possible he's walking around with broken bones.
I can't believe these guys, and their pain tolerance. If his chest looks different, best to get it checked.
if the shape looks different id consider taking him to his regular doctor who can look at it and decide if the catlige or ribs are out of place,, it sounds like its fine though because broken ribs are well known for causing alot of pain, but you say he doesnt seem to be in any.
*with apprication and respect* Jenn