I never witnessed this, but I heard these stories from very solid sources that I could trust. I was in high school in the 80s:
1) I heard the naked football practice stories a lot for guys who would forget their stuff. Maybe that's one reason I never wanted to play sports? Plus I was 6'3" and 135lbs, but anyway...
2) In college, guys who would do poorly in hockey would have to hang around naked at hockey-centric parties where girls were invited just to laugh at the naked guys...but I knew the guys and they loved it, I am sure.
3) I had a very good female friend who was in a division I college diving/swimming team. They would have co-ed, naked swim practices after the coach left every night. She said it was purely sexual-driving and they all slept with each other anyway, but it made me so jealous because she was so hot and sporty and all I ever got to see was her cycling with me in a sports bra. I used to ask her about the nude practices all the time and she liked that I asked, I think. I told her that when we go cycling, we can just change in front of each other, but she said her husband would freak, but if he didn't mind some day, she would do it just for me. Too bad I haven't seen her in a few years now.
Too good to be true, anyway.