"The Sideline View" is a YouTube channel that regularly does short film analyses from NFL games. Yesterday they took a look at Panthers RT Byron Bell and identified one of his major issues in pass protection that he must fix: his vertical set.
It is a vertical withdrawal from the line of scrimmage where you do not chase rushing defenders, but wait for them to engage you at your anchor point. This allows offensive linemen to remain square (preventing an easy loss by turning the shoulders and improper leverage in the pocket). When rushing the passer, the first step for a defender is to reach the blockers hips and gain leverage (by getting the blocker to open up a gap through turning, or by the defender getting at the same horizontal plane of the blocker). Because the blocker is moving away from the defender at relatively the same speed, he is prolonging the time it will take for the defender to execute an escape move (get past protection and get to the the quarterback/launch point).
Though it does require a modicum of athleticism (moreso than a kick-slide), anyone can perform it and be better off for it (because of the increased speed of their retreat versus a kick).
Here is the video:
I fully agree with their analysis. Bell retreats too deep off the line of scrimmage after the snap, and as a result he is not able to engage the defensive end quickly enough. This has been an issue since his rookie year - he gives too much free cushion and does not engage defensive ends quickly enough.
Dropping too far back opens up more pass rush moves for the defensive end - either inside or outside. It makes Bell more vulnerable to these moves and it also makes Cam Newton's job harder because he already has a defender in his face before he is even able to complete his reads.
For comparison watch Jordan Gross, who also uses a vertical set. Unlike Bell, watch how quickly Gross is able to engage the defensive end and win the leverage battle.
If Bell wants to improve his pass protection, he will need to fix his vertical set. If he doesn't, it could be another long year for the third year tackle.