Facebook's Mark Zuckerberg appears to get grumpy with a ref - after losing a jiu-jitsu bout. The Meta CEO was filmed fighting an unknown competitor in Redwood City in California on Saturday (6/5). Video shows the Facebook founder attempting to pin his opponent before getting pinned to the floor himself. Eventually the ref calls the match and gives the win to his opponent - believing that Zuckerberg, 38, had 'tapped out'. Onlookers say the confused and shocked billionaire is seen to be furious claiming it was an error - and the match is eventually re-cast as a 0-0 draw. The 'controversial' call seems to satisfy Zuckerberg in the footage, who hugs his opponent. Zuckerberg later won gold and silver medals at the event - his first public competition. It was revealed in September last year that he had taken up mixed martial arts (MMA), with his trainer has describing him as a "silent killer" in the ring.