Jason London's face was a broken, swollen mess following the crazy brawl at the Martini Ranch bar in Scottsdale, AZ on Sunday ... and it's clear Jason was on the losing end of the fight.

A rep for London tells TMZ ... the actor doesn't exactly remember how the violence began -- but says he DOES remember that someone had approached him in the bar and accused him of "looking at his friend's girl." Jason says the man then got physical with him.

Jason says the next thing he remembers is getting arrested ... but before he wound up in cuffs, the actor claims he was brutally assaulted by the bar's security staff ... and he doesn't know why.