Newton's First Law of Sports Motion: an object at rest is about to get its bell rung.

What you are seeing is a collision between San Francisco safety Antoine Bethea and Dez Bryant, who (in addition to being a wide receiver for the Dallas Cowboys) is a living crash test dummy. In fact, if the entire Cowboys team was put into one body, it would have looked a lot like Dez Bryant in this clip throughout the first half of Sunday's game against the 49ers, when San Francisco scored 28 points in the first quarter and intercepted three of Tony Romo's passes. There's actually an interception in this video, which I actually didn't even notice at first over the massive hit.

Sources: Bleacher Report | Digg