[Mr Mikey]

I have not shot at this type of event, but when I started shooting at a Drag strip, I approached the event staff as well as the track photographer first and explained that I was just there shooting for some friends. They gave me the track safety rules to follow, and as long as I did not get in front of the track photographer and block his shots I was given free reign to shoot. I was actually invited back by the track photographer.
You may be correct that the league photographer felt threatened by another photographer being there. If you have a friend or family member that you are taking pictures of, I would think you would have the same right as anyone else in the bleachers, just because you have a more professional camera should not disallow you from taking pictures.
You could get a copy of the league rules and see if there is anything in them that applies. You could also get in touch with the league photographer and talk to them and make arrangements for shooting at the games.
This comment may be corrected by some of the professional photographers on this site, but my understanding is that if you can recognize the person in the picture you must have a waiver signed to use that photo in any capacity, that includes numbers on their uniforms.
Good luck and I hope you get it resolved, look forward to hearing the resolution on this issue.