US stand-up comedian Dave Chappelle was attacked on stage on Tuesday during a performance at the Hollywood Bowl in Los Angeles.
Clips shared on social media showed someone running into the star.
Further videos appeared to show the comic apparently unharmed after returning to the stage at the Netflix Is A Joke Festival.
Chappelle faced criticism and protests last year when his Netflix special was accused of being transphobic.
After returning to the stage on Tuesday, the 48-year-old made light of the controversy, suggesting to the audience that the attacker "was a trans man".
According to ABC journalist Stephanie Wash, fellow comic Chris Rock - who was slapped on stage by Will Smith at the Oscars in March - then came on stage with Chappelle.
US-based British journalist Sharon Carpenter, who was also in attendance, said actor and singer Jamie Foxx joined Chappelle too.
Carpenter told the PA news agency an attacker "lunged" at the comedian as he headlined the event, sending him "flying in the air".
She said: "It looked like someone was dashing across the stage from the side. He fell backwards on to his back, with his arms and legs up in the air. He was obviously in shock. We were all in shock.
"I thought for a moment OK, is this a prank? Because they had made some Will Smith jokes. Even though Chris Rock was there, Dave was making some jokes, it was fair game, right?"
In one video, Chappelle could be seen thanking his famous friends for helping out, saying: "Whenever you're in trouble, Jamie Foxx will show up in a sheriff's hat."
"I thought that was part of the show," Foxx responded.
Chappelle joked: "I've been doing this 35 years. I just stomped a [person] backstage. I've always wanted to do that."
Jimmy Carr, the British comedian who sparked outrage earlier this year for a routine about the Holocaust in his own Netflix stand-up special, also performed at the streaming giant's event on Tuesday.
Carr tweeted afterwards to say the show was "crazy" and he was "just happy everyone's OK".
A spokeswoman for the Hollywood Bowl said an investigation has been launched, telling PA: "The incident that occurred at the Hollywood Bowl on May 3 2022 is an active investigation and we are unable to comment further at this time."
In October, about 100 people protested outside Netflix's headquarters over the airing of a comedy special by Chappelle, which they said was transphobic.
They had objected to The Closer, in which he said "gender is a fact" and that LGBT people were "too sensitive".
Chappelle later hit back at those who he said wanted to "cancel" him. "To the transgender community, I am more than willing to give you an audience," he said. "But you will not summon me. I am not bending to anybody's demands."
The likes of Seth Rogen, Snoop Dogg, Bill Burr and Pete Davidson are also starring at Netflix's inaugural comedy festival, as well as Jerry Seinfeld and recent Oscars co-host Wanda Sykes.
Tuesday's incident came five weeks after Smith famously slapped Rock on stage at the Academy Awards after Rock made a joke about the actor's wife, Jada Pinkett Smith.