So the Principal appears to be going out of his way to try to get the school sued, in a case the school will surely lose. Copyright law doesn't support him. School District Policy doesn't support him.

Not only is there no expectation of privacy at a public school sporting event, there's an expectation that cameras would be at a place like that. Parents taking pictures of their kids competing, or in their victorious moments. School yearbook or newsletter photographers. Other students. Even teammates might bring a camera, or use their phone to take a pic. Nearly everyone carries a camera around in their pocket these days, capable of doing both stills and video. Coaches sometimes have someone take video, to be able to review with the players. The sports facility may have some sort of surveillance cameras. There are probably cameras EVERYWHERE.

Maybe it would be different if it was pictures of a pickup unannounced dodgeball game in a P.E. class in the gym during school on a random Tuesday or something, but even that seems like a scenario with low expectations of privacy. But if it is a highschool football game, or basketball, or baseball, or any number of other sports that have popular teams, playing against a competing school, in the evening or on the weekend? Who really thinks that there's no chance they might get photographed if they attend something like that, Even if it is just in the background of someone's selfie or something? It is just so doubtful a court could be convinced otherwise.

The principal doesn't have a leg to stand on. If the kid sues, I'd be shocked if it even makes it to trial. With media heat and appeals to the school board, the principal will probably be ordered to back down/and or settle with the kid.