UFC president Dana White cancelled a press conference on Thursday promoting UFC 279 in Las Vegas just before it was about to start after a brawl broke out between fighters backstage.
White was booed by fans when he announced the press conference would not happen.
"It was ... crazy, I don't even know what to call it ... Twenty-two years, however long I've been doing this, we've never had an incident like today," White told reporters afterward. "All hell broke loose out. We stopped it but we didn't do a good job of not letting it happen. I don't know what went on here. It's never happened before and we'll be ready for it the next time."
Sports Illustrated reported that UFC 279 headliner Khamzat Chimaev and fellow main-card fighter Kevin Holland were the initial brawlers.
"It wasn't just one thing that erupted and happened. There were multiple things going on at the same time. ... Once it all just started erupting, it was a complete s---show."
White said the plan is for UFC 279 to go on as planned on Saturday.
Chimaev is slated to fight Nate Diaz.
"Everything will still happen. It is what it is," White said.