Raiders & Chiefs 1970. Raiders DE Ben Davidson hit Lenny Dawson when Dawson was already on the ground. Chiefs WR Otis Taylor ran back and jumped on Davidson. The brawl was one for the ages, benches cleared and it went on for 10 minutes or so. Johnny Carson even did a replay of several minutes of the brawl on the Tonight Show.
Well, that certainly explains the following 50 years...