Raja Jackson, the son of Quinton (Rampage) Jackson, a former UFC light-heavyweight champion, assaulted a professional wrestler during an independent event on Saturday in Los Angeles, according to a recording of the match.
In footage streamed live and later posted to YouTube, Mr. Jackson, 25, can be seen jumping into the ring at the KnokX Pro Entertainment & Academy event and lifting the wrestler Stuart Smith, known as Syko Stu, above his head, slamming him onto the mat and punching him at least 20 times.
Several people then pulled Mr. Jackson off Mr. Smith, who is 44. After a struggle in a ring corner, the livestream camera showed Mr. Jackson being escorted out of the building by at least four people.
On Sunday, a spokeswoman for the Los Angeles Police Department said that it was investigating but would not comment further.
Mr. Jackson, a mixed martial arts fighter, could not be immediately reached for comment.
On social media, Mr. Jackson’s father said that Mr. Smith was “awake and stable.”
He said that before the show, Mr. Smith hit his son on the head and that his son was told he could get his “payback” in the ring.
Quinton Jackson said he thought the attack was part of the show in which his son would be allowed to run in and interfere with the match as a way of resolving the earlier confrontation.
Mr. Jackson called the attack in the ring bad judgment “and a work that went wrong.” He said that as a mixed martial arts fighter, and not a professional wrestler, his son should not have been involved in the event on Saturday.
“I don’t condone my son’s actions AT ALL!” he said.
Mr. Jackson apologized on behalf of his son, who he said had suffered a concussion just days earlier, and said that he hoped Mr. Smith recovered quickly.
KnokX Pro Entertainment & Academy, the organizer of the event in Sun Valley, about 16 miles northwest of downtown Los Angeles, said in a statement on Sunday that it was monitoring the health of Mr. Smith but did not offer any further details about his condition.
“What was supposed to be a planned and agreed-upon wrestling spot turned into a selfish, irresponsible act of violence against Mr. Smith,” it said. “This egregious act is reprehensible and never should have occurred.”
The story lines and outcomes are predetermined in pro wrestling matches, which are heavily scripted and orchestrated, but not in mixed martial arts.
Mr. Smith, a veteran who joined KnokX in 2009, has said wrestling has helped him manage his post-traumatic stress disorder. A representative for Mr. Smith could not be immediately reached.
The assault appears to have stemmed from an altercation between Mr. Jackson and Mr. Smith, who, before the match on Saturday, smashed a beer can on Mr. Jackson’s head, according to a livestream.
Another wrestler then appeared to tell Mr. Jackson that he should pay Mr. Smith back with a “receipt” at the end of the match.
Mr. Smith apologized to Mr. Jackson several times.
“I didn’t know,” Mr. Smith said, gesturing to the livestream’s camera. “I thought you were a worker.”
Mr. Jackson accepted the apology and said that he understood.
Later, before entering the ring, Mr. Jackson can be heard warning on the livestream that his performance would not be scripted.
“They told me to hit him, and just leave,” Mr. Jackson said. But, he added, “I’m telling you, I’m going to hit him as many times as I can — watch.”