Will Smith hit Chris Rock in the face on stage at the Oscars after the comic made a joke about the actor's wife Jada Pinkett Smith.
Referring to Pinkett Smith's shaved hairdo, Rock said: "Jada, can't wait for GI Jane 2."
Smith walked up on stage and appeared to strike Rock before returning to his seat and shouting: "Keep my wife's name out of your... mouth."
Smith later apologised in a tearful best actor acceptance speech.
"I want to apologise to the Academy. I want to apologise to my all my fellow nominees," Smith said after winning the first Oscar of his career for playing the father of tennis legends Venus and Serena Williams in King Richard.
"Art imitates life. I look like the crazy father, just like they said about Richard Williams. But love will make you do crazy things."
The Academy tweeted that it "does not condone violence of any form".
Pinkett Smith has previously spoken about having the hair loss condition alopecia.
Rock looked shocked in the immediate aftermath of the incident, telling the audience: "That was the greatest night in the history of television."
He then handed over the best documentary prize, which was the reason he was on stage.
His joke referred to 1997 film GI Jane, in which Demi Moore played the title role with a buzzcut.
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