UFC legend Don Frye got into a physical altercation with a fan at UFC 270, punching the man in the face ... this after the retired MMA star and pro wrestler tells us the guy bumped into him and challenged him to a fight.
TMZ Sports obtained video taken at the Honda Center in Anaheim, CA Saturday night ... showing 56-year-old Frye jawing with two men as someone who appears to be security attempts to keep the peace.
Frye is seen popping the guy in the head with a jab (clearly not at full force) .