When someone is in the process of blowing up. Especially pertinent in sports when you can sense that a player is about to take the game over. They are about to become other-worldly and there's nothing anyone can do to stop it.
Think The Incredible Hulk or the Wolfman just prior to transmogrification.
It can also be used in the past tense to describe someone who completely dominated their opponent in such a fashion that made you feel somewhat bad for the other person/team.
Oh shit son, are you watching this Penguins - Capitals game? Alexander Ovechkin is on beast patrol right now, I think he might end up with a hat trick when all is said and done.
(Past tense) Man did you see what the Spurs did to the Nets last night? It was just unfair, Tony Parker was on beast patrol all night, the Nets players were like deer in the headlights whenever he had the ball. He was scoring at will on them.