What is Gap Geometry? It's a term I just made up. Some may just describe this with the more general term of gap integrity, and it certainly falls under that. It could also be described in terms of establishing the line of scrimmage. Specifically, I'm talking about what angles defenders have to each gap when defending the run. These are heavily influenced by how well the defensive linemen hold their ground (or penetrate) against offensive linemen.

I describe these angles as negative, even, or positive. Negative is the worst and positive is the best.

My purpose in this is to show the impact the level of play at the nose tackle position can have on Gap Geometry and how this affects a team's ability to defend the run.

In the illustrations below, pay attention to the nose tackle (#67) and how far upfield he is in each example. Then look at the path of the running back through the playside A-gap (red arrow) and the paths defenders would have to take to get to him if he rushes through that gap. Pay attention to the angles the defenders with the yellow arrows would have to take, how far they have to travel, how far they are apart from each other, and what blockers they would have to beat to get into the running back's path.





Negative:

The nose tackle is pushed a couple yards downfield.

The two A-gap defenders are far apart.

They both have negative angles to the A-gap.

#70 (a DT) would have to fall back and possibly dive to grab the runningback.

The LB (hard to see his number, but it's #53 Craig Robertson) would have to fight off #61's block (center Russell Bodine) to make the play three to four yards downfield.





Even:

The nose tackle is holding his ground.

The two A-gap defenders are a bit closer.

They both have even angles to the A-gap.

#70 would have to rip laterally to make a play on the runningback.

If the LB holds up vs. #61, he could make the tackle about two yards downfield. If not, he could fall off the block and make the stop about four yards downfield.





Positive:

The nose tackle has gotten an upfield push.

The two A-gap defenders are close together.

They both have positive angles to the A-gap.

#70 could fall off his block and catch the runningback a yard or two downfield. If he manages to beat his blocker with a rip or arm-over move, he could fill the A-gap and stop the runningback for a loss.

The LB can beat #61 into the gap, likely making the stop for no gain or even a loss.





Comparison of the three:





Another example:

#56 Karlos Dansby is blocked here. #58 Chris Kirksey is unblocked.

Kirksey's path to the ballcarrier gets shorter, quicker, and with fewer and fewer obstacles as the nose tackle does a better job holding up against the double team.

Dansby's path doesn't get shorter, because he has a blocker on him. A better job by the nose tackle still helps him though, because the longer and tougher path for the running back gives Dansby more time to defeat his block.





When they run the other way:

It still makes a difference, even when the runningback doesn't take a gap directly influenced by the nose tackle.

The better the nose tackle holds or gains ground, the greater the opportunity he opens up for backside pursuit by #56 (LB Karlos Dansby).

When the NT is driven downfield, #56 would have to fall back and try to catch the runner about 10 yards downfield, if he has the speed to do so.

When the NT holds his ground, #56 has a choice between dropping back to catch the back down the sideline or gambling that he can catch him from behind.

When the NT gets a push, #56 has a much clearer and shorter path to the running back and may be able to make a quick stop for a modest gain.





Altering the RB's path:

The better a defensive tackle can hold his ground or even get a push, the longer the path the runningback will have to take to get to and through the hole and the more time defenders will have to close in on him.