Cops Investigating Quinton 'Rampage' Jackson's Son Raja's Brutal Beatdown

Raja Jackson, the son of former UFC light heavyweight champion Quinton "Rampage" Jackson, is in the crosshairs of the LAPD ... after brutally attacking an unconscious wrestling opponent.

The LAPD tells TMZ ... cops were called to the wrestling event Saturday night and took a police report ... and now the incident is being investigated.

As we reported ... video shows Raja pummeling his KO'd competitor, Syko Stu, at a private wrestling event at KnokX Pro Academy in Los Angeles.

The vicious beatdown sent Syko Stu to the hospital, where an insider told us he was "fine and recovering" as of Saturday night.

A source close to the event tells TMZ they can "guarantee" Raja will never again be allowed at KnokX Pro wrestling match following what the organizers condemned as a "selfish, irresponsible act of violence."

Douglas Malo, a wrestler for KnokX Pro Entertainment and Academy, was there in the mix as he attempted to drag Raja away from Syko during the ferocious beating.

He tells TMZ he ran into the ring to try and get Raja off Syko, but he tells us Raja tried to fight him too ... going after him with a double leg attack. He notes ... "This is so shocking because they were supposed to do a small spot and before you know it, he's raining down punches."

Douglas says the whole situation was bad, "tragic" and "barbaric," and noted kids and families were in the stands watching -- including his own mother.

Rampage Jackson, a former UFC light heavyweight champion, apologized for his son's violence, saying ... "Raja is a MMA fighter not a pro wrestler and had no business involved in an event like this. I don’t condone my son’s actions AT ALL!"