UPDATE: Chris' rep just told TMZ, "Chris is not affiliated with a gang or any similar organization. He is affiliated with the Symphonic Love Foundation and other organizations that strive to bring love, hope and the arts to children in need."
Chris Brown got so pissed off over a foul call during a pick-up basketball game at a 24-Hour Fitness ... he allegedly proclaimed himself a member of the Bloods street gang and then beat the crap out of the other player.
Malcolm Ausbon just filed a lawsuit -- obtained by TMZ -- in which he claims he was playing BBall last July against Chris when he called a foul on Brown ... which Brown vehemently denied.
Brown allegedly threatened the guy saying he would kick his ass. Ausbon claims Brown then bragged that he was a member of the Bloods.
Ausbon wisely decided to back away, but Brown was on a tear. He allegedly rushed Ausbon with 3 members of his security team, who screamed, "If you f*** with Chris, you f*** with us."
The lawsuit claims the 4 men then began to "strike, punch, kick, pull and stomp Ausbon's head and body."
He says he ended up in the emergency room with injuries to his face, head, neck, back, legs and ribs. He also says he's suffering from embarrassment, fear, anxiety and post traumatic stress disorder.
Ausbon is suing Brown and 24-Hour Fitness, as well as the security team for unspecified damages.
A source close to Brown acknowledges an "incident" on the court but says there were no punches thrown.