Ultimate Fighting Championship light heavyweight champion Jon Jones and undefeated challenger Daniel Cormier were on stage in the lobby of Las Vegas' MGM Grand Hotel and Casino to promote their Sept. 27 pay-per-view headliner at UFC 178.

While the two stood forehead to forehead, Cormier shoved Jones in the neck. "Bones" then lunged forward with a punch, and the two toppled off the stage in the ensuing melee.