The Dallas Cowboys' porous run defense manifested itself in the worst way against the Green Bay Packers, as Aaron Jones looked like Barry Sanders on his way to 19 carries for 107 yards and four touchdowns.

Nevertheless, further study reveals that Dallas' issues stopping the run were bubbling below the surface prior to the team's Week 5 loss.

At first glance, it may appear as if Dallas' run defense was fine through the first month of the season. In Weeks 1-4, Dallas only allowed 96.8 yards per game on the ground -- 12th best in the NFL.

However, the lack of rushing volume was due more to game script than anything the Cowboys were doing defensively. Dallas' Week 4 contest against New Orleans was close throughout, but the Cowboys' first three games were blowouts where the opposing teams had little incentive to run the ball, as they were behind and trying to catch up throughout the game.

In reality, teams were finding success on the ground against Dallas, as evidenced by the fact that the Cowboys allowed a 51% run success rate (definition for success rate) to opposing teams -- 10th highest run success rate in the NFL -- in Weeks 1-4, per Sharp Football Stats.

Those run defense woes finally broke the surface against the Packers in Week 5, as Dallas allowed a 55% run success rate, per Sharp Football Stats. For comparison's sake, the Cowboys allowed just a 42% pass success rate against Green Bay. Aaron Rodgers was able to manifest some magic during a couple of key moments but for the most part, it was against the run where Dallas' defense was truly swimming upstream.

Therefore, with that in mind, let's take a look at why the run defense has struggled not only in Week 5 but throughout the entire season thus far.

Poor gap discipline

The No. 1 issue plaguing the Cowboys' run defense is poor gap discipline.

The Cowboys employ a one-gap, penetrating defense, where each defender is responsible for a particular gap. If every defender maintains his gap integrity and plays with the proper leverage, it creates a chain aimed at eliminating the ball carrier's paths downfield.

However, if even one defender loses gap integrity, whether it be because of a block, mental mistake, etc. -- it creates a weak link that can be taken advantage of by the opposing team.

Let's go back to Week 1 and take a look at Saquon Barkley's 59-yard run in the first quarter as an example:

On this play, Tyrone Crawford deserves the most blame for Barkley's big run. The Giants are running a duo concept toward the strong side. Crawford, who's aligned with an outside shade over the left tackle, is responsible for the C-gap between the left tackle and tight end.

Once the ball is snapped, Crawford correctly attacks the outside edge of the left tackle so that he can keep his outside arm free and clog the C-gap. However, the tight end's double team bounced Crawford inside, walling him off from the C-gap while creating congestion for Leighton Vander Esch, who is correctly filling the B-gap.

It certainly didn't help that Xavier Woods got turned by the wide receiver's block, but all it did was exacerbate the hole that Crawford already created by getting displaced out of his gap.

While gap discipline was an issue in previous weeks, it became a habitual problem against the Packers. Here's an example:

On this play, Maliek Collins deserves blame for Jones' big run. Collins, who is aligned with an outside shade over the right guard, is responsible for the back-side B-gap between the right guard and tackle.

Once the ball is snapped, Collins does a poor job reading his keys, as he fails to slide with the lateral movement of his read (right guard; No. 77) and pressure (right tackle; No. 75) keys. Instead, Collins opts to attack vertically with his initial steps, making it much easier for the right tackle to reach, hook and wall-off Collins from the B-gap.

Not only does this create a giant alley between the center and right tackle, but it also allows the right guard to climb to the second level unencumbered. It would have taken a Herculean effort from Jaylon Smith to stop this run for even a moderate gain, as he would have had to defeat a block, fill a giant alley and tackle Jones one-on-one in space - a near-impossible task for any LB.

Instead, all it took was a simple press-and-cut for Jones to get into the Cowboys secondary, where he was able to beat Xavier Woods in the open field.

Collins wasn't the only defensive tackle who had trouble with his gap integrity against Green Bay, as rookie Trysten Hill also struggled to maintain his gap versus the run. Here's an example:

On this play, the Packers are running a zone concept, and Hill is responsible for the play-side A-gap. Once the ball is snapped, instead of taking a lateral step to mirror the center's movement and maintain position in his gap, Hill attacks vertically with his first step, attacking the center's mid-line. If this center was performing a down block, this would be perfect technique from Hill; however, since the center is performing a reach block, attacking his mid-line just makes it easier for the center to expand and cross Hill's face, hook his outside shoulder and wall-off the rookie from the play-side A-gap.

This, combined with the left guard climbing and sealing Sean Lee at the second level, creates a massive hole and free access for Jones to the second level of the defense, which results in an explosive gain for the Packers offense.

LBs not covering up for DL's mistakes

While the defensive line's gap integrity has been poor, the linebackers haven't done a good job of masking the issues up front either. Because LBs are filling their gap from depth, they have a better ability to adjust on the fly.

While it's not applicable in every situation, if an LB sees a DL get displaced into his gap, he can alter his run fit to cover the gap vacated by the DT. After all, there's no point for an LB to fill his gap if there's already a defensive lineman in it. Oftentimes, you will see this labeled as 'making the DL right' during run fits. Here's an example:

On this play, it's 2nd-and-5 and Green Bay is once again running a duo concept. This time, Green Bay is double-teaming both defensive tackles.

Pay close attention to how each of Dallas' DTs respond to the double team. Christian Covington does a great job taking on the double team, as he keeps his hips square to the line of scrimmage and maintains his gap integrity. Collins, on the other hand, gets completely displaced both horizontally and vertically, creating a void in the middle of defense.

Despite Collins getting his rear-end kicked on this play, Smith still had an opportunity to stop the bleeding and stuff the RB before the first-down marker.

Technically, Smith fills his pre-snap gap responsibility; however, he failed to adjust to the changes post-snap. When attacking the line of scrimmage, Smith should have been aware of Vander Esch filling the play-side alley, therefore informing Smith to wrap backside to prevent the cutback.

Either Smith got too locked into his pre-snap responsibility and didn't adjust on the fly or he got caught guessing and the Cowboys defense suffered because of it. Either way, it's certainly not what you want from your $64 million man.

Undisciplined contain

Specifically against the Packers, the Cowboys' defense made some crucial mistakes in regards to outside contain. Here's an example:

On this play, Vander Esch is aligned along the line of scrimmage - something Dallas has done more of to combat Lee's issues when aligned on the line of scrimmage -- on the outside edge of the tight end to the short side of the field.

Once the ball is snapped, Vander Esch gets manipulated too easily by the Packers RB. All it took was the RB pressing the interior gaps to suck Vander Esch inside and create the opportunity to bounce the ball outside.

Not to be outdone by Vander Esch, Byron Jones' poor contain resulted in a Packers TD (above clip). Much like Vander Esch, Jones got sucked up by the RB pressing the line of scrimmage, putting him in poor position to react once the RB bounced it outside.

On both of these plays, the Cowboys' front did a great job of clogging the RB's running lanes before poor contain by Vander Esch and Jones respectively made it all for naught.

Trouble vs. zone concepts with designed jet motion

The #Cowboys have struggled mightily to defend zone concepts with designed jet motion. Offenses are moving/freezing DAL's LB to create favorable angles for the OL to climb and hit their targets at the 2nd level. pic.twitter.com/2Mj7wRt4ou — John Owning (@JohnOwning) October 8, 2019

The run defense has struggled to defend zone concepts with designed jet motion. The biggest problem for Dallas on these plays is that the jet motion is causing the LBs to move into compromising positions.

In essence, the Cowboys' LBs overreact by sliding too far in the same direction as the jet motion. This overreaction not only causes the LBs to initially flow away from the run, but it also creates easy angles for the offensive linemen to climb and secure their targets at the second level.

While the easy answer would be for the LBs ignore the jet motion, that would allow offenses to easily out-leverage the defense when they actually give the ball to the jet motion player on a fly, or jet sweep, creating a lot of big-play opportunities for the offense.

Now, there's a ton of different things the Cowboys can do schematically to defend these zone runs with designed jet motion, but they almost all necessitate that the LBs only slightly adjust their alignment when facing jet motion.

It's important that the LBs find the sweet spot with their footwork because if they don't react enough, they are vulnerable to the fly sweep; however, if they react too much, they are vulnerable to the handoff.

If the LBs continue to be easily manipulated by jet motion, offenses will continue to bludgeon the Cowboys on the ground.

Final thoughts

Overall, the blame for the porous run defense deserves to be spread to multiple parties.

The defensive line, specifically the under tackles, aren't reading their keys well and are losing their gap integrity because of it, the LBs are making things worse by not adjusting on the fly to what happens post-snap, and then when Dallas does bottle things up inside, they, at times, lose contain on the outside. All of this is without even discussing the issues with tackling or getting off blocks.

With the schedule getting tougher after this week, the run defense could lead to even bigger issues down the line.

Luckily for Dallas, their issues are fixable and don't require an upgrade in talent, just some technical and positional maintenance.

Enjoy this post? More film studies:

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Twitter: @JohnOwning