It's one of the few times he's standing in that movie; what you're seeing is his maximum physical exertion in the movie. Most of the rest of the movie he's behind a sniper rifle and bad guys just run into his line of sight over and over.

On the cover his head is 100% photoshopped onto somebody else's body. He's not even presentable for a still cover.

I think the joke is the incredibly poor gun-handling skills. Buttstock just waving in the air instead of against shoulder, nearly clocking himself with that deft repositioning maneuver. I'm not a gun guy, but this looks like more like The Naked Gun than a navy seal movie.