Guns n Roses Metallica 1992.
After metallica, the house lights are on while everyone is waiting for GNR. Girls flashing on the big screen and the usual stuff. In one corner of the endzone, people on the field start throwing stuff at people in the first few rows (cups, trash etc.). Pretty harmless.
It starts to spread, and within 10 minutes the ENTIRE stadium is a mass of people throwing anything they can get their hands on. HUGE toilet paper rolls flying off the upper deck, beer, trash, cups and anything you can think of being thrown. People were hiding in the hallways, and as you looked out the stadium was one big mess of sh*t being thrown everywhere. One of the most amazing things I've ever seen.
There was a profile of the GNR tour in life magazine about a month later, and they talked for a bit about the "near riot in buffalo".