by Cian Fahey

139 yards.

That is the total that Chip Kelly's offense could put up against the Seattle Seahawks defense this past week. That is 277 yards less than the Philadelphia Eagles offense was averaging entering their Week 13 game agains the reigning Super Bowl champions. It's less than half of what the team's passing game was averaging per game. That huge discrepancy in yardage was also reflected on the scoreboard, as the Seahawks held the Eagles to just 14 points when they were averaging more 31 per contest entering the game.

Furthermore, seven of those points came after a special teams fumble set the Eagles offense up at the Seahawks' 14-yard line. Even from there, it took Mark Sanchez's offense six plays and a fourth-down conversion to get the ball into the end zone.

When Mark Sanchez is involved in the complete obliteration of an offense, it's easy to shift the blame onto him. His track record as a starting quarterback in the NFL suggests that he simply isn't a good football player, and everyone knows the importance of having a good player at that position. Alas, the Eagles can't simply blame Sanchez for their struggles. Instead, the Eagles must consider the quality of their opponent and recognize how they were thoroughly beaten in every single phase on the offensive side of the ball.

For the first time since maybe last year's Super Bowl, the Seattle Seahawks defense last week looked like the machine that churned out intimidating displays on a weekly basis, the machine that held opponents to 14.4 points per game and ranked first in DVOA by a significant margin.

After 14 weeks of this season, the Seahawks rank fourth in DVOA and are giving up 18.1 points per game while being on schedule for 13 fewer turnovers over the course of the season. While they are still clearly one of the best defenses in the league, there's no ambiguity about their inability to perform to their potential. Many different elements have combined to create this defense's drop-off in performance. The departures of Chris Clemons and Red Bryant from the rotation on the defensive line were notable causes; their reaction (and those of their opponents) to being Super Bowl champions is another. Also, offensive coordinators have clearly shown off a better understanding of how to attack the team's defense after studying it during the offseason.

Which element has had the greatest impact is something that can be debated for eternity, but it appears that the most significant is very simple. The Seahawks are finally close to full health. Although Brandon Mebane is on IR because of a torn hamstring, his absence has been less significant than the return of safety Kam Chancellor and linebacker Bobby Wagner. Both Wagner and Chancellor entered the season with health issues that continued to hamper their performance during the early weeks of the regular season.

Eventually both players were sidelined for multiple games, Wagner for five and Chancellor for two. Since returning to full effectiveness on the field as a pair over the past three weeks, the Seahawks defense has been the best unit in the NFL. Before shutting down the Eagles, they held the Arizona Cardinals to three points at home and the 49ers to three points in San Francisco. If Earl Thomas and Richard Sherman are the two most important pieces of the Seahawks defense, Chancellor and Wagner are third and fourth on the totem pole.

While Chancellor is a safety and Wagner is a linebacker, each player often carries out a similar role on the field.

As explained in Film Room last year, Earl Thomas' presence at free safety allows the Seahawks to be more aggressive with their defensive alignments. This allows Chancellor to drop into the box and essentially play as an extra linebacker. On this play, Chancellor (No. 31) is lined up next to Wagner (54) in the box. When the ball is snapped, Chancellor reads the movement in front of him and immediately attacks the line of scrimmage.

Chancellor fills the running lane at the line of scrimmage, taking away one lane from LeSean McCoy. McCoy is running a designed cutback to the other side of the field, but if Chancellor hadn't reacted so quickly, McCoy would have had the option of pressing that hole instead of following the design of the play.

As Chancellor fills at the line of scrimmage, the edge defense on the other side of the field is crashing into the backfield aggressively. Because McCoy can't redirect to the running lane that Chancellor is filling, he is forced to stop behind the line of scrimmage and bounce off of his blocker. While the edge rush makes the play in the backfield, Wagner is in position to get to McCoy had he slipped through the line of scrimmage behind his pulling tight end. Wagner is engaged with an offensive lineman, but he is holding the blocker away with his extended arms while establishing outside positioning to react to any potential McCoy movement.

Wagner isn't a big middle linebacker. He doesn't excel at blowing through blockers in tight situations by using his bulk. However, within the structure of the Seahawks offense, his skill set can excel between the tackles.

On this play, the Eagles attempt to spread the Seahawks defense out and move them away from their base alignment. The Seahawks do respond by bringing Chancellor out of the box, but they don't overreact to the point that they need to drop both safeties deep and sacrifice another body into a coverage position. This means the defensive front has seven players in it to account for six blockers, one running back and one quarterback on any potential running plays.

As they regularly do, the Eagles attempt to use their quarterback as part of the running game by executing from a read-option look. This means that the offensive line immediately slides to the right at the snap and Sanchez brings his left foot backwards so he can read the defense while handing the ball off. Wagner, along with the rest of the Seahawks front, responds the way they are supposed to. All but one of the defenders in the box slide with the momentum of the offensive line, while K.J. Wright moves into position to account for Sanchez if he keeps the ball.

With Wright being held in space on the other side of the field by Sanchez's actions, the Eagles offensive line has the numbers to double-team both of the Seahawks' interior defensive linemen. Wagner has a gap in front of him, but he is reading where the football is going instead of shooting through it. The Eagles' center and right guard are the two players in position to adjust to Wagner if he tries to attack that gap. The center is successfully being occupied by the Seahawks' right defensive tackle, but the right guard is free after passing the left defensive tackle on to the right tackle.

To this point in the play, Wagner has played to his responsibilities by not overreacting to a potential run up the middle.

Though not aggressive against the inside run from the start of the play, Wagner still has the short-area burst to accelerate through the line of scrimmage and meet McCoy in the backfield. He is too fast for the right guard who attempts to knock him down as he slips past him. The negative side of Wagner moving at this speed is that McCoy can more easily slip past his attempted tackle. Wagner is unable to bring McCoy down, but he forces the runner sideways and slows him down to the point that the rest of the defensive front can converge on him before he can get to the second level of the defense.

This kind of athleticism and discipline allows Wagner to be effective as a run defender between the tackles, but it really highlights his ability in space.

On this play, Wagner is initially lined up with Wright over the middle of the field. He is to the left of Wright, over the offensive line's B-gap. When Chancellor drops closer to the line of scrimmage, he forms a trio with Wagner and Wright, pushing Wagner to the C-gap outside of the offense's right tackle. Despite the pre-snap motion, Wagner isn't drawn in any direction at the snap. Instead he reads the offensive line in front of him and follows the pulling right guard into the flat. His speed allows him to get to the outside of the tight end who tries to block him, then his hand usage lets him knock the tight end downfield while moving towards the flat.

In the flat, Wagner meets pulling left tackle Jason Peters at the line of scrimmage. Wagner isn't strong enough to take on Peters' block, but he doesn't need to beat him to have a big impact on this run. Instead of beating Peters, Wagner only has to occupy him early to prevent him from getting ahead of McCoy downfield. Importantly, he does this on Peters' outside shoulder to set the edge and force Darren Sproles back infield where there are defenders to contain him.

Wagner's success against outside runs is based on controlled aggression. He understands how to read plays as they develop to locate the football on a consistent basis.

We can see on this play how Wagner stays in line with Sproles as he moves across the field. He always has his body in position to plant and turn with the running back if he cuts back infield while also still moving at speed towards the sideline. He shows good awareness of where he is going to avoid running into a potential blindside block that would take him out of the play. Once he gets outside of the confines of the defensive line in front of him, Wagner needs to work his way through a pulling offensive lineman in space to get to Sproles.

The incoming blocker attempts to cut Wagner down as he moves across the field. Wagner, showing off his awareness, is able to adapt to the movement and use his hands to push the blocker away while moving towards Sproles. Wagner meets Sproles close to the line of scrimmage to prevent him from gaining more than 1 yard. On this kind of play, Wagner's lack of size isn't an issue. Instead, his athleticism and discipline allow him to close on the ball with relative ease.

When your running game is attempting to create space by exploiting the opposing defense's lack of athleticism and discipline, Chancellor and Wagner aren't players you want to see on the other side of the field. The Eagles were only able to rush for 56 yards on 22 attempts because of the Seahawks' team speed and execution on the day.

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They were only the latest team in the league to learn how effective the Seahawks' second-level run defenders can be. Over the past three weeks, the defense has given up just 62 rushing yards per game. For the season as a whole, they rank third in run defense DVOA.

Both Wagner and Chancellor show off consistent, controlled aggression in every facet of their play. Wagner's features in coverage as much as it does in the running game, but Chancellor in particular stands out when given the freedom provided by his situation.

As much as playing with Sherman and Thomas affords Chancellor opportunities to play to his strengths, Chancellor himself highlights the value of what Sherman and Thomas do by excelling in his role. Chancellor is known for his ability to deliver heavy hits over the middle of the field or even on rare occasions when he lines up as the deep safety. Those big hits show off Chancellor's incredible athleticism, but it's his awareness and control that allows him to deliver them. That awareness and control can be seen on plays that are considered less spectacular also.

On this play, Chancellor initially lines up as the strong safety over the offense's right tackle. When Jeremy Maclin motions across the formation, Chancellor follows him so that he is just outside of the left tackle roughly 8 yards from the line of scrimmage. The Eagles are running a screen play to Maclin on which Chancellor is able to close behind the line of scrimmage. Importantly, Chancellor beats the offensive linemen to their spots after reacting to the screen at the right time. He wasn't simply overplaying the screen and opening himself up to being taken advantage of by a fake.

Playing the underneath routes and making tackles from a distance while being disciplined is an impressive trait, but maybe less impressive than Chancellor's ability to play the ball at the catch point.

Too often, bigger NFL defensive backs who are capable of landing big hits prefer to attack the wide receiver rather than the ball. Chancellor may not play the ball as well as the best cornerbacks in the NFL, but for a player of his size his ball skills are exceptional. As we can see on this play, Chancellor understands how to break on the football ahead of receivers in front of him without risking an unnecessary penalty.

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In 2013, the Seahawks had a great defense. Great defenses aren't built on one or two stars and a bunch of role players. Great defenses need high quality players all over the field. When you remove just a couple of those players, the quality of the overall unit can't be sustained even for short stretches. With Wagner and Chancellor back to their best, the Seahawks have a chance to be great again. While their last three games have been exceptionally impressive, especially keeping Chip Kelly's offense to 139 yards, greatness isn't established over a short period. The Seahawks need this level of play, or something close to it, to be stretched into the postseason.

If that happens, it's hard to think this team won't have a chance to repeat as Super Bowl Champions.