I play on multiple USTA tennis teams- two that are just wrapping up their spring/summer seasons, two that are almost ready to start the late summer/fall season. To participate on any of those four teams, USTA required that all players sign a Covid-related waiver.

I can see the NCAA mandating that schools cannot yank scholarships or otherwise penalize players who chose to opt out or not sign a waiver... but telling them they are not allowed to sign a waiver, period, seems like it would be illegal. If you're 18+, you have the right to make that kind of decision for yourself.