If the league photographer has a contract there are a few things to be aware of;
1. That exclusivity clause is not binding on anyone except those who were a party to it. In other words, if some other photographer - ie parent, friend of player wants to shoot then there is nothing that is enforceable upon them - they were not a party to the contract.
2. The team photographer has a right to shoot because he is most likely giving a percentage to the league. That's normal and it helps support the league.
3. The OP does have the right to shoot anywhere he wants to - but the sticky point is when he begins to charge for his work. NO DOUBT that the parents asscoiated with the league know that a photographe has been contracted.
4. No need for a release from each player - because there is no expectation of privacy and it is a public place. Unless the OP decides to use these images as stock or for advertising. Portfolio usage is OK.
5. The LEAGUE can restrict who shoots at their events, but it usually requires posting the restrictions somewhere, and making the information available to everyone easily.




