From the headline you already know what happened here. A supremely pissed off bodybuilder threw a temper tantrum and slapped the shit out of a judge after he didn't win his competition.
Here's some more context: The bodybuilder Giannis Magos was actually declared the winner of the 100kg division and figured he had the 2016 IFBB Diamond Cup Title locked up. Well, he didn't.
Magos wasn't declared the overall winner and when he came across judge Armando Marquez he put the paws on 'em, as shown in the video clip above. Furthermore, he also reportedly trashed the judges tables and pulled his dick out, though all of that was cut from the video.
