Its standard thing to do in America for virtually every high risk activity; skiing (defacto with your lift ticket by state laws or skiing would have gone bankrupt decades ago), sky diving, mountain biking, paragliding, etc etc. Playing football during COVid is absolutely high risk. Heck, you can't play HS sports in CT w/o signing an acknowledge about concussions.
Without a waiver and at least an acknowledgement, I don't see how any clear thinking University President moves forward until we have a vaccine which could provide some cover. And if kids don't want to sign them I completely understand why. The waiver establishes the participants knew the risks and went forward anyway. There is still room for recourse, but it does become harder for the signee.