It’s up over at Grantland:
At the snap, the Chiefs line up with one wide receiver, a fullback set to the offense’s left, and a tight end and H-back to the right. The strong side of the formation is to the offense’s right, but the fullback to the left is in position to block someone on either side. This presents a problem for the defense. Because they keep two safeties back (not pictured), they have a difficult time matching numbers to each side of the offense’s formation. Not counting the center and defensive nose guard, there are three defenders to the offense’s left to deal with three potential blockers, and four defenders to the offense’s right to deal with four potential blockers. But the counter trey brings two blockers from the backside to completely overwhelm the defense at the point of attack. (And, of course, the defense already had issues in not having counterparts for all of the offense’s blockers.)
Read the whole thing.