Date: 12/8/1980
Game: New England Patriots @ Miami Dolphins

It's not too often that live sports broadcasts are looked to for the latest (non sports-related) breaking news, but this night many people first heard of John Lennon's assassination through Monday Night Football. During a timeout, MNF announcers Howard Cosell and Frank Gifford discussed whether making the announcement was the right thing to do and after some convincing, Cosell informed the nation once they came back on the air. The slain Beatles member had actually appeared on Monday Night Football in December of 1974.