A Washington Football Team fan unloaded on a fellow fan in the stands during the team's game against the Chargers on Sunday ... dropping haymaker after haymaker on the poor guy.
In the footage of the melee, filmed by someone sitting near the violence, you can see a man in a Clinton Portis jersey began scrapping with another guy in a Sean Taylor uni.
Unclear what started the tilt ... but the man in the Portis jersey quickly got the upper hand -- and never let off the gas pedal until other fans finally intervened.