I shoot weddings, so I always have friends and family members who are shoting away with everything from a P&S to FF DSLR. If they aren't professionals, they don't often think about the fact that they might be in your shot. The problem with this guy is that he has a website - so clearly he is more than someone's brother looking to take a few pictures for mom and dad's wall of fame.
My guess is that he feels entitles to be wherever he wants. For some reason he feels as though he is credentialed as much of you. If he is at the next game, I would go up to him and ask him who is shooting for. If he is freelancing and hoping to make a couple of bucks by selling to parents, then just explain that you are credentialed to be there and that you don't mind if he is there, but that he needs to stay out of a credentialed photographer's way. Since he was kind of snarky with you before, I think you should be a little snarky back
If he is there shooting for someone, then I would explain that you are also there for the same reason and that you will need to find a way to shoot without getting in one another's way. If he doesn't have the gear to get the close up that he wants without being right on the court, that is his fault and he should have to deal with those consequences.