Rock was presenting an award during the Academy Awards ceremony Sunday when he made a joke about Smith's wife, actress Jada Pinkett Smith, and her close-cropped hair. Pinkett Smith shared her struggle with alopecia, which causes hair loss, in December.
Smith responded to the joke by striding up on stage and slapping Rock in the face. The actor then returned to his seat and yelled to Rock, "Keep my wife's name out of your [expletive] mouth!"
Kimmel, who hosted the Oscars in 2017 and 2018, said on Jimmy Kimmel Live! that he initially thought the moment was staged.
"I was watching like most people, and I said to my wife, 'They did a really good job with that punch -- it looked so real,'" Kimmel recalled. "And about three seconds later, we realized it was because it was real."
Kimmel called the incident "so shocking" and compared the moment to a boxing match.
"The only thing I can really compare it to is when Mike Tyson bit [Evander] Holyfield's ears," he said.
Kimmel also jokingly called the moment "the old Hitch slap," referencing Smith's film Hitch.
On The Late Show, Colbert poked fun at Smith by saying the slap wasn't the worst thing the actor has ever done.
"That is the worst thing Will Smith has ever done... Wait, forgot about Wild Wild West. I'm kidding, the worst thing he's ever done is Gemini Man," Colbert said.
On Late Night, Meyers called upon writer and The Amber Ruffin Show host Amber Ruffin to comment on the slap.
"I know why they don't have a category for best horror movie, because the best horror movie is the Oscars," Ruffin said.
Ruffin said that she, like many, took to social media after the incident.
"I scrolled Twitter and I read jokes and thinking pieces and opinions about it and while I felt I had seen something horrible and private that made me feel great shame, I found out everyone in America felt the same way I did. And that my friends is the magic of the Oscars!" she said.
Fallon opened The Tonight Show by celebrating his in-house band leader Questlove winning the Oscar for Best Documentary for Summer of Soul moments after Smith slapped Rock. He then addressed the slapping incident.
"Seriously, you know it was a strange awards show when it ends with a statement from the LAPD," Fallon said.
Questlove also addressed the moment, saying he was meditating before he won the award and was initially unaware of the confrontation between Smith and Rock.
Smith apologized to Rock in a statement Monday on Instagram.