The fight appears to have been set off when Paul says that Diaz, an MMA fighter, hasn't accepted his offer to fight in a cage after their boxing fight.
"I'm coming to MMA and i'm going to f--k you up," Paul yells at Diaz.
Diaz then jokes that the "bully" is the robot on stage who he says he smacked with a beer can.
Then they went to the face-offs and that's where all hell broke lose.
The face-offs were completed but neither man walked off stage. Instead they began jarring again. We can't really hear what's said but Paul turns back to the media as Diaz and his team start to walk off and says, "He's a b***h."
Then on the other side of the stage, everyone began shoving. Massive security guards rushed the stage and separated the teams. It doesn't appear as though Diaz or Paul ever came to blows with each other though.