Several supercross fans got into a wild skirmish on Saturday night -- and it all appeared to start because a woman showed her boobs to the crowd.
The crazy scene all went down at the Anaheim 1 Supercross event at Angel Stadium -- when in the upper rows of the venue, a women flashed her bare chest while holding her beverage with her teeth.
Another woman seemed to be so pissed over the sight ... she left her seat a short time later and confronted the fan, complaining about the topless move.