You get your facts straight. Obviously he has the right to shoot; however, you also insisted he has the right to sell. If the league has a contract with another photographer, you'd be wrong. So instead of stating "you have the right to sell YOUR photos as well", as you flippantly did, the proper action would be to contact the league and ask them.
The league may have an exclusive contract with a particular photograph. That means only that photographer would have access to the prime vantage points which the league may control (if they've so contracted with the local government).
But a contract between the league and the photographer has absolutely nothing to do with any other photographers. We've gone around about this with school prom photography. A school might have a contract that permits only one photographer to shot prom shots at the school's premises, but that has nothing to do with other photographers having a "special prom session" at their own studios on the same night.
If another photographer has a vantage point outside the area controlled by the league, that photographer is free to shoot what he can see.
He is also free to sell those photographs to the parents without a release. A model release is only needed for commercial use, which states define as meaning "soliciting business or products," and not the sale of the actual photographs themselves.

If he isn't there, I would just go shoot all I want. If he is there, you walk to him and telling him that a verbal contract worth squat in the court of law. Tell him to leave you alone and you both shoot the same game. Hopefully you have better gear and perspective to generate more sales. Now, if he is too unconcern about having a written contract, I would predict that he would leave you alone or at least he would avoid shooting the same game with you. 
