The Seahawks host the Cowboys this weekend at the CLink and the matchup pitting Seattle's stout run defense against Dallas' dominant run game should be a major key. Through five games, the Cowboys have racked up a NFL-best 800 yards rushing on the legs of DeMarco Murray and behind a stacked offensive line. Lining up across from them, they'll find a Seahawks unit that's given up a paltry 2.6 yards per carry and 249 yards total, both tops in the league.

So, who will budge first?

"Their running game is very consistent and they're very strong upfront," Pete Carroll told reporters on Wednesday. The Seahawks' defensive-minded head coach was especially effusive in praise for DeMarco Murray, noting that "He's really special and he continues to break really solid tackles. Guys have him and he keeps on moving, and keeps on going. He's got enough speed to run around you, and set you down and bust away from you. He runs through tackles, he runs up inside very well, he's good on the perimeter.

"So it's going to be a great challenge for us, and we had a really cool week of preparing for the run."

Because I wrote about Dallas' run game last week, I thought a good followup would be to break down the foundation of the Seattle run defense, a unit and scheme that's been very good over the past few years. This matchup will be strength on strength, and the team that can gain ground superiority will probably end up winning this game.

So, let's run down the basic principles, along with video examples.

TENETS

Effort

This is the big thing that Carroll preaches consistently. It's a coaching cliche, of course, but for the Seahawks' defense, "maximum effort on every snap" really shows up in how quickly each player pursues, closes on the ball and hits. Effort also shows up in Seattle's swarming tackling style and "finishing" attitude.

Discipline

Of course, you can't just fly around all willy nilly. There are very specific sets of rules within each scheme, meaning each player must do his job, avoid getting hooked or reached, get off blocks and win the battle in front of him. While the Seahawks play fast on the field, I'd also classify them as a patient defense, particularly against the run.

Tackling

The Seahawks got some pub this offseason for their decision to bring in rugby players to teach proper tackling techniques that don't involve the head, and they take all of this very seriously. Read more about that here.

Power up front to rebuff push

The Seahawks "go big" in base downs with the rotund 6'1, 305-pound Brandon Mebane at the nose tackle spot and a combination of Tony McDaniel (6'7, 310) and Kevin Williams (6'5, 311) at the three-technique and five-technique spots, respectively. This trio, along with nickel defensive tackle Jordan Hill, has proven to be very stout against the initial offensive line surge, repulsing double-teams or seal blocks while holding ground on the line of scrimmage (or even pushing the LOS back toward the quarterback). As they say, it all starts in the trenches. These interior horses and their ability to take on and get off of blocks allows for Seattle's linebackers to fill and tackle.

Power on the edges to force inside

Seattle mixes schemes on the outsides, but Bruce Irvin is generally at the strongside linebacker spot right now, acting as the force player to the inside, usually lined up outside the offense's tight end. This player cannot lose leverage to the outside and must force all runs back in toward his cohorts. He gets beat outside, and it's a big chunk of yardage, so these SAM linebackers must be able to take on and defeat blocks from both tackles and tight ends. K.J. Wright plays on the line at that spot at times, as does O'Brien Scofield or even strong safety Kam Chancellor.

Continuity, congruity to fill gaps

Playing run defense has an element of randomness to it because you can have players "in charge" of certain gaps (the space between each offensive lineman or tight end), but gaps become pretty fluid when you have 5-to-7 offensive players all moving in unison or at fractured angles. Run defense is like an intricate dance, and if your players aren't working off of each other to maintain gap integrity and fill new gaps that are being created fluidly, you're going to get gashed.

This is where patience comes in. You can't have defenders that are too eager to crash into gaps or miscalculate where the runner is aiming. At the same time, you have to have players that can stack and shed (get off of blockers) while keeping their vision in the backfield so they can peel off the correct direction to make the tackle.

Speed to make up for errors

Finally, one thing that makes Seattle pretty strong as a run-defending team is that it has excellent speed at the linebacker and safety positions. Inevitably, someone is going to fill in the wrong gap or get hung up on a block (or taken out by an oncoming blocker), so it helps a ton to have players that can mitigate this issue with their makeup speed. Did a running back get outside past a force defender? Having the speed to run him down at linebacker is a big help.

Hey, how bout some pictures and GIFS! Those are fun!

Base 4-3 Under defense

Here below, you'll see Seattle's "under" front. The "under" denotes that the strength of the defensive line is actually tilted away from the strong side of the offense (with the three linebackers tilted toward the strength side).

So, in this case below, you can see Washington has lined up with its tight end aligned to the right of the formation, and in response, Seattle has NT Mebane in a one-technique alignment over the center, DT McDaniel heads up on the guard (two-technique) and Michael Bennett outside at the "wide nine" (nine-technique) alignment. On the strongside of the offense, five-technique Williams is lined up inside Irvin, who is playing the strongside linebacker spot, walked-up to the line of scrimmage. Seattle does other fronts, but this is its "base" look, at least this season thus far.

Seattle frequently stacks the box with eight defenders, and this is the case below (with Earl Thomas the eighth defender, a de facto linebacker in this case). K.J. Wright is the weakside linebacker, and Bobby Wagner is the middle linebacker.

Let's see this dance in real-time.

First key in the success of this play for Seattle: the defensive line gives up little to no ground vertically, while at the same time getting down the line horizontally to string the run along. This is exceedingly tough. It looks fairly easy above, but it's not. At all.

No. 92, Mebane, is a player to watch here to hammer that point home. He pushes the center back into the run lane, causing Alfred Morris to slightly alter his trajectory outside. Mebane manages to keep his feet under him as he runs with the blob of humanity moving down the line, as do his cohorts in Williams (No. 94) and McDaniel (No. 99).

On the play-side edge, watch Bruce Irvin manhandle tight end Logan Paulson. This won't be quite as easy for Bruce against Jason Witten, of course, but above, Irvin gets the job done, forcing Morris to take an inside track (leads him into a huge pile of people). The Redskins run more wide zone than any other team in the NFL, but it's also a staple in the Cowboys' offense, so Irvin's a key player to watch this week.

Let's check out an example that goes the other way. Same deal -- the defensive line holds its ground for the most part, and Seattle's linebackers set the edge, take on blocks and fill the now-opening gap. K.J. Wright even manages to force a fumble, which is recovered by the offense.

In the case above, Washington pinches down with its tight end, which means No. 93, Schofield, has to be the force player against left tackle Trent Williams, not an easy proposition. He does a well-enough job.

Ok, here's another example. The Seahawks roll strong safety Kam Chancellor up to the line as the force player on the strongside, leaving Irvin on the weakside of the formation.

Here's why they trust him to do that. He sideswipes the oncoming fullback, who is meant to seal him from the play, and makes the tackle.

It's fun to watch Bobby Wagner through this play, because you can really get an idea of how a MIKE linebacker must adjust to a fluid gap structure on the offensive line, keeping his eyes in the backfield and filling where needed. If you watch both Wagner and Wright, this is a great example of the type of aggressive patience you need to play sound run defense.

Rewind to Week 3's game between the Seahawks and Broncos, and you see a similar look from Seattle, who put six on the line, marching Chancellor up to the strong side as the force player. As noted above, the 6'4, 230-pounder has no issues with this role. In fact, he revels in it.

What you see above is great pursuit down the line (the nose tackle, Brandon "Banger" Mebane, makes the tackle), a great edge set by Chancellor against Julius Thomas and patience by the linebackers.

Defending the run in nickel

All teams these days dabble heavily in nickel defenses, which means they either replace a linebacker or defensive lineman with an extra defensive back. Obviously, this is to better match up against three and four-wide receiver personnel groupings, but it also makes a defense more susceptible to the run (defensive backs are just not typically as tough to block).

Here's an example of Seattle's nickel defensive personnel. They've swapped out a linebacker for a third corner, and now have Irvin down in a three-point stance as a pass-rushing defensive end.

Of course, same principles still apply.

This is kind of a weird pitch play with a lead-blocking tight end for the Packers, but the Seahawks defend it well. Defensive tackle Jordan Hill does a nice job of holding up against a double team, which allows Wagner and Wright the freedom to read the play and react. Wagner quite easily defeats the blocking tight end to share a tackle with Chancellor, who comes down from the second level.

Another example below: All the tenets at play. Hold the edge, hold at the point of attack. Linebackers and safeties fill.

Eddie Lacy sees No. 50, Wright, fill in what should be the target crease, and is forced to try to bounce it outside. He runs right into the force player, Schofield.

One more example, which more or less just shows a lot of the same. Getting off blocks, flowing to the football, swarming and maximum effort.

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The Seahawks have been pretty strong in run defense over the past few seasons, but their pace thus far is better than anyone expected.

When Carroll was asked if the Hawks had done anything different this year than in previous years, he replied, "No; I do feel like the continuity of our guys, and the familiarity of what we're trying to get done," are the main factors.

"Brandon [Mebane] may be playing the best he's played," said Carroll. "He may be at the top of his game right now. Tony [McDaniel] played really well last week too and Kevin [Williams] in his spots. Those guys are really strong upfront -- they allowed Bobby [Wagner] and K.J. [Wright] to just make all kinds of plays. Bruce [Irvin] was a factor. The whole front group is functioning really well; we're not doing a lot of special stuff, we're just trying to play really good base defense and great technique and play really solid ball there."

After giving up an average of 62 yards rushing per game over their first four, Seattle will face by far its biggest test this week against Dallas. The discipline, effort, and tackling they've shown so far will be key.