The Bills' struggles on the field have apparently frustrated Buffalo fans so much, they've now turned on each other -- getting into a violent fistfight at the game on Monday night.
The wild scrap happened at some point during Buffalo's loss to Denver at Highmark Stadium ... when several fans clearly became upset with a man in a Josh Allen jersey.
It's unknown what sparked the commotion ... but you can see in video shot by someone a few rows away from it all, fists started to fly just seconds after words were exchanged.
Check out the clip ... after the Allen fan got tagged in the face by a jab, he threw some haymakers -- which led to an all-out melee.
At one point, a man in a Thurman Thomas shirt jumped in to try and help out the Allen fan, which led to even more chaos.
Thankfully, it appeared cooler heads prevailed after just a few moments of fighting.
We've reached out to cops to see if any arrests were made, but so far, no word back yet.