We had something similar happen years ago. I wasn't involved, so I don't know the exact details, but it sounds similar to yours. The schools said the locker room would be locked, our guys checked the door when they went out before the game and at halftime, and somehow money was gone between halftime and the end of the game.
In our case, the school did offer to reimburse the guys. Legally, I don't know if there was any liability on their part, but they offered and our guys accepted.