Clipper Darrell -- the most famous L.A. Clippers fan -- was knocked out during an altercation at a game on Monday ... new video, obtained by TMZ Sports, shows.
In the footage, you can see Darrell -- real name Darrell Bailey -- in his famous half-red, half-blue suit ... standing with a Crypto.com Arena security guard following the Clippers' game against the Boston Celtics.
The two seem to be in some sort of argument ... where the man wearing a red polo appears to be preventing Clipper Darrell from moving through a concourse at the NBA arena.
At one point, the man can be seen in the video putting his elbow near Darrell's neck in what seems to be an effort to keep him from advancing. Darrell, the footage shows, then swiped at the man's arm to get it off of him.
That's when the man in the red balled up his fist and swung on Clipper Darrell -- connecting straight with the superfan's jaw.
Darrell crashed into a nearby trash receptacle ... and appeared to lose consciousness.
Crypto.com Arena President Lee Zeidman tells us ... the altercation all started after the security officer tried to direct Darrell and other departing fans to nearby exits.
"Clipper Darrell became involved in a verbal and then physical altercation," Zeidman said. "After receiving immediate medical attention, Darryl was transported to a nearby hospital for further evaluation and treatment."
"An investigation of the incident was launched which determined the employee’s behavior to be a direct violation of our training and approved responses resulting in the immediate termination and arrest of the employee by the LAPD."
Clipper Darrell told us on Wednesday morning he's suffering from headaches ... and is still in a lot of pain. He added that he's currently on medication to try to alleviate some of his symptoms.
Sources close to the Clippers, meanwhile, tell us the team is aware of the incident.
Clipper Darrell has been a Clips season ticket holder for two decades -- and has gained notoriety for loudly leading taunts and cheers throughout L.A. games.