First of all it sounds like you have done a great job raising your son. He sounds like the kind of kid I love to coach. Second of all as a coach I will pick up on this sooner or later either by seeing it or hearing it or one of my Seniors will let me know whats going on. When I do get wind of it the problem will go away or the player will. There is absolutely no place for it on a team. It could be that this kid feels threatened by your son. If your son keeps working and keeps a great attitude he will be there in the end. I have had kids like this in my program before. But they dont last. The cream will rise to the top talent wise and attitude wise. Bad kids like this have a way of eliminating themselves from the equation.