The MMA fighter who beat up TWO guys in a bathroom stall in a WILD brawl caught on video is telling TMZ Sports why he was attacked in the first place ... and it's INSANE!!!
The man at the center of the scuffle in the s**tter is ex-UFC fighter Jason Knight -- who now competes in the Bare Knuckle Fighting Championship.
In other words, HE'S THE WRONG GUY TO FIGHT IN A BATHROOM!
Knight tells us ... he was taking a leak at a club in Mobile, Alabama back in December when he heard two other guys in the bathroom complaining about their wives.