I think the dirtbike symbolizes the machine-like power and unyielding aggressiveness of the Bears defense; their powerful rage and their contempt for the conventional, staid, boring norms of the average NFL defense. Either that, or it's a guy that thought to himself, "HOLD ON, MAN, I'MMA GET MY DIRTBIKE IN THIS THING! YEE-HAW!" One of the two.
And here's the same thing, performed by more attractive, more female people, who should try it again wearing fewer clothes.




