The team represents the school and is an entity of the school. As such, I think the school can put the pressure on the team, and the coach (I also assume he is a school employee) to ... not "operate outside the school system" without the school's permission.
However, my guess is, they should not be able to close down your web site. As long as you are not the "official" web site, and you state that clearly, I don't see how they can demand your shutdown.
However ... the team and the coach could be in a lot of hot water if they continue to "co-operate" with you.
And now that I've given my opinion ... seek legal counsel from a REAL lawyer. A brief consultation should not cost very much. Some lawyers even give you the first 15 minutes or so for free. It could save you a bundle of money AND headache down the road.
Maybe one of the parents is a lawyer ...
The Old Sarge