He would have been one of those guys who was in and out of juvie in high school and prison afterwards because he would be flipping his shit at every little thing and punching people and smashing things.You're right, if he played football he'd probably be in prison by now. It's ironic, Robert is one of the best examples of "toxic masculinity" I've ever seen. Can you imagine his personality and anger issues with a physically capable body?
I don't think he could handle the discipline of a professional sport long enough to play football for long. Bizarro universe Musclebob would probably throw a punch at the coach after getting into an argument with him. The physical version of when he tried to pull evil genius mind games on his counselor.