Khabib Nurmagomedov retained the UFC Lightweight Championship with a fourth-round submission of Conor McGregor Saturday night at T-Mobile Arena, but that it wasn’t the real main event.

After McGregor tapped out from a rear naked choke, Nurmagomedov jumped over the cage and into the crowd, starting a melee that quickly involved fans, fighters and law enforcement personnel. It was a scary scene with Nurmagomedov’s team, McGregor’s team, rival fighters and fans brawling outside the Octagon. Security worked for several minutes to restore order as the pro-McGregor crowd booed Nurmagomedov, who improved to 27-0.