Pitt - PSU, 1981, Pitt Stadium. There is no doubt in my mind that this game was the largest attended sporting event ever in the city (but could not be officially announced, due to fire code standards). If the official capacity of Pitt Stadium was 69,400, then there were easily more than 75,000 folks there that day. The student section was largely packed beyond reasonable, with folks standing/sitting in every aisle. There was a guy who hung out at Peter's Pub who supposedly made/sold several thousand bogus tickets himself. Hell, people climbed on top of the restrooms on the upper ring just to see, as they were like 5-6 deep packed in the walkway of the upper ring, above the bleachers. We were #1 in the country, and had already accepted the Sugar Bowl bid. Enormous game.
Still perhaps the most dejected I've ever been after a sporting event.