Gap Control: Interior Defense, 2011

| 5 years ago

Gap Control: Interior Defense, 2011

Whether you have defenders playing one gap or two, whether you aim to contain a running back or flush him outside and fly to the ball, the run D constant remains: you must keep contain and maintain control over every gap. One lapse in a gap, one misread, one piece of overpursuit and the control a defense has over seven other gaps is ruined–the runner scampers through the weak side C-gap that the back-side linebacker flowed away from.

We here at Pro Football Focus are in the fortunate position of not only being able to look into our grades to discover which defenses excel in run defense, but thanks to our statistical harvesting we can also nail down where defenses excel. Who locks down the middle and prevents opponents from gaining easy A-gap yards? Who throws a blanket around the outside and makes it tough to spring big plays off the edge?

Having already looked at the offensive side of the ball, we now turn our attention to the defensive side where we start with inside run defense. Here we will look at who succeeded and who failed in shutting down the A-Gaps (rushes to either side of the center) and the B-Gaps (to the outside shoulder of the guards) in the 2011 regular season.  


A-Gap Assassins

Where better to start than right up the middle, the shortest path to the line of scrimmage and yards gained? If you can’t stop teams from running through the A-gaps then you aren’t going to be able to force them into more complex offensive plays that you might be able to pick apart for your own gains. There are many different ways to skin a cat when defending the A-Gaps: one big body at nose tackle, two big bodies crashing inside or even a big middle linebacker flying downhill. What matters is getting the job done and there is no one dominant scheme in the Top 10 A-Gap defenses from the 2011 season–3-4’s, 4-3’s and hybrids all slot in.

The common theme here, however, is that the Top 3 defenses defending the A-Gaps (by yards per carry) all came from the AFC North and all went to the playoffs. It’s little wonder that the Browns were among the 10 worst A-Gap rush offenses when they faced the three best A-Gap defenses in six of their sixteen games last season. The Steelers even managed to have great success defending A-Gap rushes in spite of the fact that their nickel package has no nose tackle, in theory opening up the inside to solid gains. It is a credit to the rest of the front seven that they covered for the absence of Casey Hampton–or any inside presence on the line–when the Steelers were forced into sub packages.

Three defenses went without allowing a rushing touchdown on A-Gap carries. Unsurprisingly, one of those is the ever-stingy 49er run defense with the other two residing on the East Coast in the shape of the Jets and the Redskins. Of the Top 10, only two came from the NFC and the entire AFC North was in the Top 6 at preventing yards after contact through the middle of the defense. If you want to gain yards through the middle on an AFC North team, you are going to have to block exceptionally well, and on top of that, your running back will have to work very hard. No cheap yards here.

TeamAttemptsYardsYards per CarryYards after ContactTouchdownsLongest Rush Allowed
Baltimore Ravens1163012.6174212
Cincinnati Bengals1012772.7178310
Pittsburgh Steelers1264083.2255126
New York Jets1113613.3223017
Jacksonville Jaguars1143823.4258219
* NFL Average1074193.9248235


A-Gaps Assaulted

At the other end of the league, you find that the weakest teams through the heart of the defense reside in the NFC. The conference housed the five worst A-Gap run defenses, though clearly this wasn’t a devastating trait as two of the five teams made it to the playoffs. The two worst, both from the NFC West, gave up more than 5 yards per carry through the middle of the defense. The St Louis Rams, firmly at the bottom, surrendered a 91-yard run up the middle, emphasizing their inability to shut down a rush after an offense had taken a lump hammer to their interior.

Their division rivals in Arizona spent much of the season imitating the Pittsburgh Steelers with a nickel package that did not have a nose tackle or any strong inside presence. As a result of that, the Cardinals (despite not giving up a huge run to skew their stats) were consistently found wanting in the middle where the Steelers were not. Second-year player Dan Williams graded positively as a run defender, but played fewer than 200 snaps and simply could not have the positive effect on their A-Gap efforts enough of the time. Moving forward, the Cardinals either need to re-think the deployment of their personnel or they need more from the inside linebackers coming straight downhill to cut off those gut carries. Right now, the Cardinals are showing opposing offenses a weak under belly to the run game when forced into nickel packages.

As with the strongest defenses in the anti-A-Gap game, the weakest are not marked out by scheme; the bottom five featuring both 4-3 and 3-4 defenses. Two teams from the AFC East (each showing indecision over their defensive front in 2011) allowed the most rushing touchdowns on A-Gap carries with the New England Patriots and the Buffalo Bills both allowing five. Six teams allowed a carry of 50 yards or more through the A-Gaps this season with the Rams not alone in an inability to shut teams down once they had broken through the first line of defense.

TeamAttemptsYardsYards per CarryYards after ContactTouchdownsLongest Rush Allowed
St Louis Rams1095685.2296491
Arizona Cardinals904515.0227237
Detroit Lions1004944.9346150
Chicago Bears894304.8199488
Green Bay Packers703344.8245354


B-Gap Berserkers

On average, defenses saw less action through the B-Gaps (to the outside of the opposing guards) than they did coming straight at them through the A-Gaps. But, at 4.5 yards per carry, rushes off-guard were significantly more effective than rushes right up the middle. Through the B-Gaps you find more opportunities for linemen to down block on opposing defensive linemen; driving immediately into the side of defensive players and forcing second level defenders to fill that gap, potentially meeting a pulling or lead blocker.

Five teams didn’t allow a single touchdown off-guard this season with, again, unsurprisingly, the 49ers being in that group joined by division rival Seattle along with playoff foes Denver and Pittsburgh and the Kansas City Chiefs. As will become a theme as we move outside, the 49ers were among the league’s best in controlling this gap, allowing a league low of 3.2 yards per carry on B-Gap carries. They didn’t allow an average of more than 3.5 yards per carry through the A-, B-, C-, or D-Gaps in the 2011 regular season. Their ability to play with a lead and force teams to the air also helped their B-Gap run defense as they faced a league-low 58 carries off-guard this regular season, almost 70 less than the Bills who saw a league-high 125.

The 49ers are joined in the Top 5 B-Gap defenses by some expected names like Houston and Pittsburgh, but also by one unforeseen team in the shape of the New Orleans Saints. This was the one gap on their defense that the Saints defended better than the league average, letting up fewer than four yards per carry. They did, however, see only 63 carries; one of only three teams who saw fewer than 70 carries off-guard–simply because of their inability to defend rushes off end (more on that in our next article).

A special mention here for the Chiefs who were fifth in the league in yards per carry allowed in spite of seeing the second-highest number of B-Gap carries last season. Only the Bills’ defense was more heavily tested, but the Chiefs D stood up to the task and did so consistently, allowing fewer than 4 yards per carry and not allowing a carry of 20 yards or more through this gap all season.

TeamAttemptsYardsYards per CarryYards after ContactTouchdownsLongest Rush Allowed
San Francisco 49ers581853.2120018
Houston Texans832943.5177125
Pittsburgh Steelers843213.8170014
New Orleans Saints632413.8145323
Kansas City Chiefs1144393.9218019
* NFL Average944254.5245237


B-Gaps Bashed

If teams pick out a weakness in a defense, they go after it mercilessly. Given that, it’s not shocking that only one of the five worst B-Gap defenses in the league last season (all giving up over 5 yards per carry there) saw fewer than 100 B-Gap carries. The one exception was a Redskins defense that allowed those chunks on only 65 carries against, with no excessively long run to skew their average (their longest allowed through a B-Gap was 43 yards, only just above the league average). If the Chiefs stood up to the constant barrage of B-Gap carries, the Redskins got off lightly as teams failed to exploit a weakness.

Buffalo and Tampa Bay had the dubious honor of leading the league in touchdowns allowed through these gaps, letting up seven and six touchdowns, respectively, directly off of the guards. Neither, though, features in the worst five on this list. Tampa Bay allowed 5.0 yards per carry, but fell just short of the fifth spot held by the fortunate Redskin defense.

An interesting name on this list is the Denver Broncos. How, one might ask, could a team with the best run defending tackle from the 2011 regular season, Brodrick Bunkley, have such poor defense through an interior gap. With Bunkley playing predominantly in 0- and 1-Techniques, aligned around the center, he was routinely in such a position that teams could down block with their guards and seal him out of B-Gap rushes. The Broncos’ poor defense of gaps (that Bunkley was in poor position to defend) will certainly raise questions over their ability to withstand his loss during the 2012 season.

The worst B-Gap defense, fresh from being among the best A-Gap stoppers, was that of the Cincinnati Bengals who allowed more than 5.5 yards per carry off-guard. This is almost three full yards more per carry than they allowed inside of opposing guards. The Bengals’ flaws can be laid squarely at the door of the right side of their defense as opponents gained 6.6 yards per carry there and both of the Bengals’ B-Gap touchdowns allowed came from that spot as well.

To fully illustrate the Bengals’ problems with finishing plays through this gap, they gave up 223 yards after contact (4.1 yards per carry after contact). So even when Bengal defenders reached a ball carrier through the right side B-Gap, they allowed a significant continuation after that first contact. Woeful control of one gap, that yards after contact figure of 223 is more than 13 defenses allowed through both B-Gaps combined.

TeamAttemptsYardsYards per CarryYards after ContactTouchdownsLongest Rush Allowed
Cincinnati Bengals1015685.6421259
Denver Broncos1126275.6288047
Cleveland Browns1126235.6313267
Indianapolis Colts1116135.5286456
Washington Redskins653345.1200143



So, in a passing league does a quality interior run defense mean anything anymore? Well, the Top 3 A-Gap run defenses and the Top 4 B-Gap run defenses all went to the playoffs. The playoffs, in the end, showed that even with the proliferation of the passing game, this league is still about balance and stopping inside runs is still a part of that. Not stopping the inside run to the extent that it harms the rest of your defense by overcompensating is, in itself, alarming. The best defenses–the likes of Baltimore, Pittsburgh, San Francisco, and Houston at the top of these lists–controlled the heart of their defense without having to draw players inside or blitz the inside gaps so frequently that it hurt them elsewhere.


Other articles in this series: Outside Defense | Outside Offense | Interior Offense


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| Director of Analysis

Ben joined Pro Football Focus in 2007, and has since been in charge of the company’s analysis process. He also contributes to PFF’s weekly NFL podcast.

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