He was a few songs into his set when he stepped to the edge of the stage, and then suddenly tumbled 4 feet onto the cement. Turns out there was a small gap between the speaker and the stage that Vince didn't see and he fell through the crevice onto the floor.
We're told Vince, who has battled with alcohol addiction, had not been drinking. It was just an accident.
He's struggled on stage in recent years ... in May he pulled the plug on a show after his voice gave out. He's also been criticized for underwhelming solo performances, but he was doing well Friday night until the accident.