First Chip Kelly was going to outrun the NFL. Then, after a 1-3 start, Chip Kelly was overwhelmed by the NFL. Now, with the Eagles a win away from being in the playoffs in Kelly's first season as coach, Kelly is a genius again. Funny how that works.


Most of the attention paid to this season's turnaround has Fun-adelphia Eagles' fast-paced, fast break offense. But Chip Kelly's scheme putting up points isn't exactly a surprise: LeSean McCoy is one of the best running backs this season, and Nick Foles has quarterbacked with shockingly few errors after usurping Michael Vick. The loss of Jeremy Maclin hurt, obviously, but even short a few hands, the Eagles were never really starved of offensive weapons.

The more interesting part comes on the other side of the ball: In 10 of the Eagles' last 11 games—and we'll talk about that unexpected blowout loss to the Vikings later—the defense has allowed 21 points or fewer. This is the same team that gave up 93 138 points in its first four games of the season, and the front seven deserves a lot of credit; it's been revamped, with a few additions complementing the young leftovers from Reid's regime. How's it hitting its stride right now?


The Scheme

In their last two years under Andy Reid, the Eagles attempted to run a wide nine front helmed by offensive line coach-turned-defensive coordinator Juan Castillo. (Edit: The wide nine was the project of defensive line coach Jim Washburn, although Castillo was overseeing it.) That experiment worked in 2011, but fell apart the following season, when the Eagles ranked last in pass defense DVOA and gave up 126.3 rushing yards a game. The team finished 4-12, and the house was cleaned.

When Kelly was hired, he brought in Billy Davis, the Browns' linebackers coach, as his defensive coordinator. Davis incorporates a hybrid defense called the Predator. Sheil Kapadia of Birds 24/7 wrote a great piece back in February on what the Predator looked like, using stills from the Seahawks, who run a similar formation. To sum it up—although you should read Kapadia's explanation—when used, it appears to be a 3-4 but works as a 4-3.

In the Predator, the 3 in the 3-4 consists of the nose tackle, one standard 3-4 defensive end, and one DE who actually plays as a DT, to help the nose tackle. When that happens, the outside linebacker on the same side comes down to act as a defensive end. This allows the Eagles to bring blitzes from either side. Let the nose tackle handle the center and left guard to try and keep the ends from being doubled. And then, if the outside linebacker comes down, any missed block by the offensive line could wreck the whole play. It emphasizes variety.


Greg Bedard of MMQB.com talked to Davis, and he was proud of his extremely young defensive line, explaining how they give opposing o-lines "multiple looks," as in, various possibilities to worry about. As Bedard points out, there's more movement from the linemen than usual in a base 3-4. It leaves less room for error in terms of blocking, because if the offensive linemen don't get everything exactly correct, their quarterback or running back can end up on the ground behind them.

This is true of any play, but in a league that values disguising coverages, disguising actual positions is the logical evolution. Let's look at how this thing works.


Defensive Line

Peace out, Cullen Jenkins. Safe travels, Mike Patterson. Get the fuck out, Jason Babin. Philadelphia's defensive line turned over almost completely in just one year. Babin was waived during the 2012 season; Jenkins and Patterson signed with the Giants. Their replacements came cheap. Draft picks Vinny Curry, Bennie Logan, and Fletcher Cox, as well as Cedric Thornton, who was undrafted but has stuck to the Eagles since 2011, are the key guys in a now-solid rotation of enormous dudes up front for Philly.


Logan, the rookie defensive tackle, isn't going to garner consideration for any awards, but he's been a solid nuisance in this scheme, especially considering his size for a 3-4 tackle. Logan's listed at 309 lb., roughly 20-30 pounds lighter than a normal nose tackle. His smaller stature doesn't allow him to meet the requirements for a true 3-4 nose, but he's played well, and after defensive tackle Isaac Sopoaga was traded to the Patriots in Week 8, Logan saw an uptick of snaps, specifically at the nose tackle spot. Of his 22 tackles, 18 have been stops, otherwise known as a failed play, according to Pro Football Focus.

But it's the defensive ends who really power this defense. Because Chip Kelly hasn't built this team from the bottom up, he's had to improvise with the available groceries. Cox and Thornton switched from 4-3 defensive tackles to 3-4 ends, and change has been good for them. For one, more time on the field has helped: Cox had only 526 total snaps as a rookie, and he's had 826 this season with a game to go. Thornton had 406 in 2012; he's nearly doubled his snap count this season with 702. Naturally, the position changes meant more opportunities to show up on the stat sheet. Thornton was rather ineffective with eight hurries and 15 stops in 2012, but this year, he has 15 hurries and 35 stops, sixth-most among 3-4 ends. Cox had four sacks and 14 hurries, and this season he has three sacks and 39 hurries, second-most among 3-4 ends.


Vinny Curry, meanwhile plays a minor, but key role. He's almost exclusively a pass rusher. Approximately 71% of his 299 snaps have called for him to blitz. The rest of the time, he's stopping the run.

The line's adjusted yards number (rushing yards directly attributed to the line, not the rest of the defense) is 3.93, 19th in the league. It's been a productive yet unspectacular season for the Eagles' D-line. Their real job is to unleash the true strength of the defense, and the Predator system.


Linebackers

Where the defensive line falters, the linebackers do not. They've been brutal to running backs that break through, surrendering only 0.99 second-level yards, fifth-least in the league, according to Football Outsiders. And in open-field yards, the Eagles have given up just 0.35 yards, least in the NFL. Chip Kelly is all about not giving up brutally big gains on defense, and his philosophy has rung true in terms of the run defense.


The biggest offseason signing on defense was linebacker former Texan Connor Barwin, and though he hasn't been the same pass rusher he was with Houston, that's not due to a lack of effort. Barwin's only accrued five sacks in 2013, but he has seven quarterback hits and 30 hurries, most of any Eagles linebacker. At the very least, he's bringing pressure. The sacks will come. Barwin's best work has come against the run; he's totaled 30 stops, in the top 10 for 3-4 outside linebackers.

Opposite Barwin is Trent Cole, formerly the defensive end with the confusing-ass 58 on his jersey. Now he's doing the same stuff from the linebacker position. Coverage is not Cole's bright spot; he's seen only one-eighth of his snaps on passing plays. Otherwise, he's stopping the run or blitzing. Cole's rushed the passer on 48.7% of his snaps and has 40 stops, second-most of any 3-4 outside linebacker. The Eagles rank in the middle of the league with 37 total sacks, but Cole leads his team with eight, and most of those have come recently. In the past six weeks, Cole has sacked the quarterback seven times, second of any player besides Justin Tuck (7.5).


The other starting two in this four are inside linebackers DeMeco Ryans and Mychal Kendricks, who have played nearly all of the available snaps. But while they've been solid in run stopping, something has to change in terms of coverage, because they've been flat-out bad. Ryans leads the team with 120 total tackles—Kendricks in second with 94—so they're sniffing out plays, but also whiffing on a sizable amount. Kendricks has 21 missed tackles, tied for first among inside linebackers; Ryans has 13. At least the duo can stop the run, but their defense against the pass is rather awful.

Weaknesses

Now that we've talked about how the defense has worked, we must mention a game in which it decidedly did not work. What happened against the Vikings, in which the Eagles gave up 48 points? The run defense performed well, allowing just 51 yards on 30 carries to Matt Asiata. (He might have had an awesome day for fantasy teams, but Asiata only averaged 1.7 yards per carry.) The pass defense was the main weakness. Matt Cassel threw all over it for 382 yards and three touchdowns.


Even when the pass defense gives up gains, it's still about bending and not breaking with Kelly. The Eagles defense gives up 32.89 yards per drive, but per FO, they also rank eighth in the league in terms of turnovers caused per drive (.185). Teams like the Packers and Patriots have succeeded with this mentality. (The longstanding assumption is that a great offense will put a defense in more favorable field position, and thereby give it fewer opportunities to "break.") As long as defensive players are containing and not missing tackles, drives can stall, and the Eagles can hand the ball back over the the offense, which was never much of a problem for Kelly and the Eagles.

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