Everybody has to worry about run fits. New South Carolina defensive coordinator Jon Hoke mentions them each week when he is interviewed. After practice on Friday he was asked to explain some more for the less technically savvy fan. Here’s what he had to say:

Well you know there is an A gap, a B gap, a C gap, and a D gap when you break it down at the end of the day. And when you are an eight man front everyone is responsible for a gap, so you got to fight to control your gap.

To elaborate on his explanation the first thing the defense has to make sure it can defend against is the run. The offense has to run the ball through the space between its lineman called gaps. Before the play, each defender has responsibility for a gap. (Some defenses use two gap responsibility, but that’s another topic and not what Hoke is doing this year.)

The offensive formation will alter some of the gap responsibilities, but the fundamental principle remains the same: every gap has a defender who will theoretically stop the ball carrier from running there. Having a defender for every gap is the first half of a run fit. Here are the gap responsibilities of South Carolina for one play against Kentucky.

Screen Grab Credit: SEC Network

All of the gaps are covered, but that’s only half of a run fit. The second part is controlling the gap. To control the gap the defenders have to control the inside half of the gap. They cannot allow themselves to be pushed out, or worse, back.

The gaps are nice and clean before the snap, but as the play develops they can get bigger. Fitting the inside half of the gap is where the defender needs to be to stop a run from coming through there. Here is the same play a few seconds later.

Screen Grab Credit: SEC Network

This play was very successful for Kentucky. On the play side (the left side of the diagram) look at the A gap. It’s gone, so no running back will be running through there, but the defense doesn’t have gap integrity there. The defensive tackle is being pushed back and away and is directly across from the center.

Because the A gap defender is being pushed out of the play, look at the size of the play side B gap. The linebacker is going to have to make a good play to handle that big hole and a lead blocker (#86). He doesn’t, and the play goes for about 20 yards.

Run fits are often confused as just being gap responsibility, but they are more than that. Look at the South Carolina defensive tackle who had responsibility for the A gap. An uninformed observer may think, “he’s doing his job; the A gap is closed.” However, because the A gap wasn’t closed properly, the B gap is now huge.

When coaches are talking about run fits, they are talking about being sound in lining up; they are talking about being sound in technique and attacking the proper part of the gap and the offensive lineman, and they are talking about not being blocked. It’s all of those things.

Thinking about it another way: t he offense is going to try to move defenders around, push a lineman this way, block another one that way, and if they are successful, holes will develop in the defense. The philosophy and technique of not allowing that to happen through gap control is what the coach means by run fits.