I had never seen this before at the Rose Bowl but about halfway through the Maryland game, the section of empty seats on the sunny side in Section 8 got filled up with shirtless (male) fans. First it was a few, then more joined, and kept joining, until practically the entire section was filled with shirtless, towel-waving UCLA fans. It was so fun to watch the section fill up with enthusiastic Bruins! Ironically, this could only happen because there was an empty section that they could assemble in so for once, it was beneficial not to have a sold out stadium. It also looked like some women tried to start their own section next to the men, but I only saw about 5-6 at most. Maybe this will be a new tradition?
Apparently this is a trend? Here's an article talking about this.