49ers X’s and O’s Lab: Stopping the Run, Run Fits and Jim O’Neil’s Run Defense

December 20, 2015; Santa Clara, CA, USA; San Francisco 49ers inside linebacker NaVorro Bowman (53) tackles Cincinnati Bengals running back Giovani Bernard (25) during the first quarter at Levi's Stadium. Mandatory Credit: Kyle Terada-USA TODAY Sports
December 20, 2015; Santa Clara, CA, USA; San Francisco 49ers inside linebacker NaVorro Bowman (53) tackles Cincinnati Bengals running back Giovani Bernard (25) during the first quarter at Levi's Stadium. Mandatory Credit: Kyle Terada-USA TODAY Sports /

There has not been much talk about the San Francisco 49ers new defensive coordinator Jim O’Neil, but today we look more in depth at his run defense, break down how defenses play the run and examine what went wrong in Cleveland last year.

One of the least talked about aspects of the San Francisco 49ers this offseason is their new defensive coordinator Jim O’Neil.

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I’ve written about O’Neil here and here, but briefly, the former defensive coordinator oversaw the 23rd-ranked defense (27th against the pass, 26th against the run), according to Football Outsiders metric, DVOA.

O’Neil’s lack of success was due in part to injuries to cornerbacks Joe Haden (concussion), Justin Gilbert (concussion), defensive end Desmond Bryant, safety Tashaun Gipson (ankle), and linebackers Craig Robertson (ankle) and Scott Solomon (ankle).

However, the Browns’ struggles were also highlighted midseason, which caused some alarm among players and fans, and concerns that fans now should not overlook:

"Recently, a number of players have told me what they believe is the main impetus behind the continual running-back beatings: The Browns have issues with gap integrity—football speak for jamming the holes between the offensive linemen.Rather than being assigned specific gaps, Cleveland’s defensive linemen play different techniques based on how their offensive counterparts are blocking them. The linebackers, then, are expected to guess what technique their teammates are using, scrape through the resulting mess and make the play. Opposing offenses have identified this flaw on film and are repeatedly, week-after-week, gashing the edge of Cleveland’s defense. It’s a completely chaotic approach to stopping the run, and players have said—off the record—they’re spending way too much time thinking, and not nearly enough time reacting.“It’s an entire guessing game,” said one source. “Imagine trying to define mud.”"

So were Cleveland’s defensive struggles in the running game a problem of talent or a problem of scheme?

It is really a combination of both, but the more problematic thing is the way the run defense was coached to play their assignments. We’ll soon go to the film to find out but first we need to examine how a defense is coached to stop the run.


Run fits for a defense describe the assignment each defender is coached to play in a given play call. Each defender is responsible for a gap and, when executed properly, each defender works in harmony to clog every possible running lane and limit the gains a running back could make. How does each player do this?

By filling roles as the spill/pursuit players, force/contain defender, alley/fill defender, and the contain player.


The spill or pursuit player are the players who are coached to force the ball laterally to the outside. The role is usually filled by the interior defensive linemen and inside linebackers. They fill their gap with the squeeze technique, or moving toward the ball carrier making their specific gap smaller, thus closing a potential running lane.

By “squeezing” their assigned gap, they force the ball-carrier to “spill” east or west. If unable to penetrate the backfield for a stop, the defender(s) will aim to at least bounce the ball carrier outside.

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With the spill defenders sending the runner to the outside, the “force” or “contain” defender (usually defensive end, outside linebacker, or even a defensive back) will attempt to funnel the ball carrier back inside toward the interior defensive linemen or an open gap to a scraping linebacker.

The force defender has to set the edge, often doing so against the block of the run side tackle or tight end; If unable to shed his blocker, he must to maintain outside leverage on him while remaining square to the ball carrier. If taken too wide, a dangerous running lane will emerge between the force defender and the closest spill defender.

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Any gaps not already occupied by the spill and force defenders need to be plugged when the ball carrier is forced back inside. The alley or fill defender is that man and they are responsible for clogging any gap in the middle that the spill and force defenders have not already occupied. If the spill and force do their job, they’ll force the ball carrier into a gap being filled by a scraping linebacker.

The alley defender can be a safety in the box, or the nearest run support defensive back, or a free linebacker. If the ball carrier cuts back through this more or less intentionally created running lane, the alley defender must be in position to make the tackle.

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If all of the above is executed soundly, the ball carrier should cover more yards running side-to-side than upfield. The spill/pursuit will force the ball carrier to the outside, where the force/contain will force him back inside, only to be met by the alley/fill defender. If just one part breaks down, the result is usually a solid gain by the offense due to an alley that resembles more of an expressway than a tight running lane.

The below image illustrates the basic defensive line gaps and techniques.

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Let’s go to the film and see where O’Neil’s Browns struggled.

In Week 5 versus the Baltimore Ravens, the Ravens line up in 12 personnel (one running back, two tight ends and two receivers). The play called is an outside zone to the left with Javorius Allen as the running back. The Browns line up in a 4-3 under front with the nose tackle in a one-technique and the under tackle in a 3 technique.

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4-3 Under defenses try to do two things: stop the run and pressure the pass. It uses 1-gap techniques to do so, which means that it relies on penetration and disruption of the offensive line. Defenders aligned in a gap in any front are typically going to one-gap their gap in front of them as crossing the face of an offensive lineman is exceedingly difficult if not lined-up directly in front of their man.

The alignment of the 4-3 Under is meant to funnel strong-side runs to the “will” linebacker. The defensive line and “sam” linebacker all have to control their gaps at the line of scrimmage, allowing the “will” and “mike linebackers to make plays.

The way the defense aligns should allow the “will” to be free and unblocked as well as funnel runs to him. The leading tacklers should be the “will” and “mike,” similar to the 3-4. On weak-side runs, both the “will” and “mike” should be flowing to the play-side for mop-up duty.

Back to the play.

Several things stand out. As I touched on earlier, a defensive lineman aligned in a gap is supposed to shoot that gap by pinching or squeezing. However, what happens on this play is the defensive line gets caught man on man and does not adequately squeeze the gaps.

We’ll start with the defense’s left side of the line.

Nose tackle Danny Shelton (No. 71) in the one-technique position gets caught up with the right guard and spills the running back to the outside away from the scraping “mike” linebacker Karlos Dansby (No. 56). The Ravens effectively neutralize two defenders right away.

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But the most glaring mistakes happen on the right side of the defensive line, or the Ravens’ play side. Defensive lineman Randy Starks (three-technique, No. 94) and Armonty Bryant (nine-technique, No. 95). Starks takes on the left guard with absolutely zero leverage, a weak first punch, and squeezes his gap right into the double-team, preventing the “will” linebacker Tank Carder from scraping through his gap.

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Defensive end Armonty Bryant also gets ridden out of the play by not staying square to the line as the force defender and instead lets the Ravens tight end neutralize him by attacking his play side, inside shoulder, allowing the ball carrier to find the seam in the void that was to be filled by Bryant, Starks and Carder.

The result of the play is a 44-yard gain for the Ravens.

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There are any examples of this type of “read and react” taught by O’Neil that creates confusion. In O’Neil’s scheme, defensive linemen are taught to react to the offensive line rather do what the 4-3 defense is meant to do: control the gaps. Instead, O’Neil coaches his players to react to the block rather than simply control their gap. This creates confusion for the linebackers and makes the offensive line’s job much easier to execute.

In week three versus the Raiders, defensive tackle Starks is once again the culprit. The Browns are again aligned in a 4-3 under defense.

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The Raiders run a zone run to the left with an arc block, but running back Latavius Murray finds the cutback to the right and a seam in the Browns defense.

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Starks (three technique, No. 94) is supposed to read the blockers in front of him and use “block-down step-down” technique to defeat the block of the left tackle blocking down. Instead of squeezing his gap, Starks gets a weak punch and this immediately puts him at a disadvantage by carrying his weight forward and taking him off-balance.

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This enables the Raiders double team to “scoop” block and reach the second level and into linebacker Craig Robertson (No. 53).

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Robertson thinks he’ll be able to pinch his gap and make the play but the double team guard comes off and gets in his path and opens up a lane for Murray as he picks up 54 yards.

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The final play we’ll examine (and one that is covered more in depth, courtesy of Orange and Brown Report) is a perfect example of a scheme where a player is asked to think too much instead of just reading and reacting mixed with overall schematic weakness to compound the issue.

In Week 9 against the Bengals, the Bengals line up in a 11 personnel (one running back, one tight end and three receivers), and the Browns again line up in a 4-3 under one-gapping defense with the strength of the defense set to the one, five, and nine-gap side (reader’s left side in the GamePass image).

The Bengals run a toss play to the left with a “pin and pull” block to the playside with the tackle and guard pulling to seal the edge and the tight end blocking down.

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Linebacker Barkevious Mingo takes an inside step upon reading the tight end’s down block. In this situation, he is coached to use the “block-down step-down” technique, squeeze his gap and get his hands on the tight end to disrupt the block.

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This step takes him right into the pulling linemen. At this point he should rip through and utilize the “wrong arm” technique and attack the lineman’s up-field shoulder. This should spill the ball carrier outside where a scraping linebacker can make the play.

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Linebacker Karlos Dansby takes a good angle to scrape into the D gap, but he must cover too much ground and the defense is out-leveraged on the play side.

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The Browns did have some decent defensive talent when healthy and were a strong defense when former head coach Mike Pettine had a say in the final scheme.

It will be interesting to see how the O’Neil utilizes the 49ers front seven and if the talent can overcome some these coaching issues. During OTAs and minicamp, there were already reports of the scheme being more complicated than it was under Vic Fangio and Eric Mangini. This does not bode well for a young defensive unit.

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I previously predicted the 49ers would play a base 4-3 defense but, after those articles, O’Neil was quoted as saying the 49ers would remain a base 3-4. Whether or not O’Neil puts them in a position to succeed is entirely another question.

O’Neil will certainly have a long way to go to overcome his coaching deficiencies if he hopes to succeed with this scheme. There are quick fixes to these positional and alignment errors, but it remains to be seen if and how he will correct them.

Fans should not lose hope though, because this defense has some great young talent that will complement the scheme and coaching.

Next: Jim O'Neil and the 49ers Pass Defense

All images courtesy of NFL.com and NFL GamePass.

All statistics, records and accolades courtesy of Pro Football Reference unless otherwise indicated.