Amid the confusion, members of the Russian's team then jumped inside the cage and started throwing punches at McGregor, hitting him in the face. "That was disgusting," commentator Joe Rogan said. "It's so incredibly disappointing."
Months of personal taunting appeared to explode — and UFC president Dana White opted to escort Nurmagomedov out of the cage instead of presenting him with the belt.
"If I put this belt on you, everyone's going to start throwing s*** into the Octagon," White said.
White later revealed three men have been arrested and are being taken to jail.
"I don't even know what to say right now, I'm just disgusted and sick over it," White said.
He said McGregor was not hurt. "He's upset about the fight," White said. "Not about the fight after the fight."
Nurmagomedov exacerbated several months of hostilities between the fighters' camps by stepping away from a prone McGregor and immediately pointing at the Irishman's corner, shouting and throwing his mouthpiece.
The men in McGregor's corner appeared to respond with taunts, and Nurmagomedov climbed over the fence and fought with Danis, a Bellator welterweight who trains with McGregor.
While McGregor watched, two men entered the cage and sucker-punched him. He was forced to defend himself before security personnel separated everyone.
Nurmagomedov now faces a nervous wait to find out what repercussions he'll face. Commentators have already speculated about him having his title stripped, facing heavy fines and suspension — and even losing his US green card.
"There's a lot of repercussions for what they did tonight," White said.
The bad blood came after McGregor attacked a bus while attempting to confront Nurmagomedov at a UFC event in New York in April. He threw a trolley and a bin at the window of the bus, smashing glass and injuring other fighters.
He was arrested and later pled guilty to a charge of disorderly conduct.
This is what happens when you stoke religious and ethnic tension as part of the promotion for an MMA fight. Unfortunately, this is not likely to end here #UFC229