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Weak spot in Eagles' defensive approach leaving unit vulnerable

The Philadelphia Eagles entered this season as plausible favorites to win the NFC East, and they were widely expected to be a Super Bowl contender, led by a promising young QB, a deep roster assembled by one of the most well-regarded front offices in the league and a head coach revered by the analytics community for his fourth-down aggressiveness. Fast-forward two months, and the Eagles sit at 4-4 with just a 38.2 percent chance of making the playoffs (per Football Outsiders), with their likeliest path to the postseason being to win the division (they have a 32.6 percent chance of doing that vs. a 5.6 percent chance of claiming a wild-card spot). Spirits are surely thus not too high in the City of Brotherly Love, given that the Dallas Cowboys already have a 3-0 divisional record and a half-game lead overall.

The offense has had its fair share of issues this season, but the deficiencies with this team are most apparent in a hobbled defense that has fallen far from ranking fifth in DVOA in 2017, when the unit helped bring Philadelphia its first Super Bowl. The defense looked OK in a key road win over the Buffalo Bills in Week 8, but the fact remains that the only two opponents the Eagles have held below 24 points thus far were quarterbacked by Luke Falk and Josh Allen.

The Eagles' defensive woes can be attributed to a perfect storm of problems with roster construction/scheme, philosophy/personnel and pass rush/coverage. And while injuries have certainly played a major role, we should note that the Eagles' defense was also decimated by injuries last season, measured as having the second-most adjusted games lost (71.3) by Football Outsiders, and yet served as a competitive unit, ranking 15th in DVOA.

To understand what has broken down in this defense, we first must review its structure and objective. Simply put, defensive coordinator Jim Schwartz's No. 1 priority is to stop the run, as highlighted in this terrific breakdown of the Eagles' defensive philosophy by Benjamin Solak. In a league where passing is more important than ever, that commitment to the run game can present problems if the secondary struggles to hold up on the back end.

Schwartz is known for his single-high safety looks and corresponding middle-of-the-field-closed (MOFC) coverages (a.k.a., Cover 1 and Cover 3). The charting data from Pro Football Focus backs up his reputation, as the Eagles' defense has shown a single-high pre-snap safety look at a top-six rate in each of the past three seasons: 72.3 percent of plays in 2017 (sixth), 74.7 percent in 2018 (fourth) and 71.0 percent this season (fourth).

As Solak explains in the aforementioned article, Schwartz rolls out single-high safety looks so he can roll a safety into the box with run fits in mind. Schwartz emphasizes one-gapping penetration by his four defensive linemen, and in order to have a defender for each gap in run responsibilities, Schwartz will often match blockers in the box with an extra defender in the box. As a result, the Eagles rarely employ light boxes (which is when there are six or fewer defenders in the box). According to Next Gen Stats, the Eagles' defense used light boxes at the sixth-lowest rate both in 2017 (44.6%) and 2018 (49.2%), and they've dropped that to 39.2 percent this season, the lowest rate in the NFL.

The number of defenders in the box shows a strong relationship to score differential. Since 2017, defenses that are losing employ light boxes -- or play to stop the pass -- on 47.5 percent of plays when losing compared to 64.4 percent of plays when winning, per Next Gen Stats. This makes intuitive sense, as the opponent of a losing defense is more likely to run the ball to maintain its lead, while the opponent of a winning defense will more often elect to throw the ball to catch up. Defenses will adjust their box counts accordingly.

Given that the Eagles have been trailing on 50.3 percent of their defensive snaps this season (the seventh-highest rate in the NFL), one could assume that their tendency to avoid light boxes (or play to stop the pass) is biased by game script, as they would roll out heavier boxes to stop offenses that are expected to run on them while the opponents try to protect their lead. When losing in 2019, the Eagles have employed light boxes on 27.2 percent of defensive snaps, the lowest rate in the NFL. However, while teams league-wide run slightly more often when leading, this is not the case against the Eagles. Rather, Eagles opponents pass (136 attempts) more often than they run (114 attempts) when leading, which seems to be the result of Philadelphia's intentional defensive philosophy to try to dissuade opponents from running, regardless of score.

By refraining from using light boxes, Schwartz has succeeded in deterring offenses from electing to run. This followed a general trend that has held true since 2017. Opposing offenses elected to run on the Eagles on just 33.1 percent of their plays in 2017, the lowest rate in the NFL. Game script surely played a role, as the Eagles' defense also was losing on just 11.4 percent of its snaps that season (the lowest in the NFL). However, the Eagles also had the lowest run-rate faced (34.5%) in 2018, and that season, they trailed on 33.5 percent of snaps (15th-highest rate in the NFL). This season, the Eagles' opponents have run on 37.8 percent of snaps (ninth-lowest rate in NFL), still much lower than expected, given that, again, Philly has trailed on 50.3 percent of its snaps.

While it discourages offenses from running the ball, the Eagles' single-high structure often puts the outside CBs on an island without safety help over the top. This has helped them earn their reputation as being susceptible to routes involving double moves. According to PFF, defenders aligned as outside CBs for the Eagles have been targeted on these routes 36 times since 2017, eight more than any other team. These targets have resulted in 15 receptions (most in the NFL), 377 yards (second-most) and seven TDs (most in the NFL).

The single-high structure lays a heavy burden at the feet of the outside corners, as Eagles defenders aligned as outside CBs have been targeted on 35.6 percent of their coverage snaps since 2017, the highest rate in the NFL by a significant amount. In fact, the gap between the Eagles and the Packers (second-highest target rate for their outside aligned CBs, 31.8 percent) is larger than the gap between the Packers and the 21st-ranked 49ers (28.5%). Part of this also can be attributed to talent level. The Eagles have eschewed investment in cornerbacks (bottom seven in each of the past three seasons, per Over the Cap). The Eagles' outside-aligned CBs have been a below-average unit in coverage as graded by PFF in each of the past three seasons, although this season, they have been especially bad, with a 46.3 grade (fourth-lowest in NFL).

That being said, the Eagles have survived without expensive and elite talent at the CB position in the two previous seasons, so something else must be going on. Let's consider some striking trends from Next Gen Stats. First, the pass rush has become less effective in each of the past three seasons. The Eagles had the quickest time to hurry (2.64 seconds) in 2017, but that time has increased to 2.85 seconds in 2018 and 2.97 seconds this season. Offenses have also started throwing the ball deeper, increasing from 7.3 air yards per attempt in 2017 to 8.0 in 2018 and 8.8 this season.

Looking at the heat maps below, which show the Eagles' completion percentage allowed above NFL average by location on the field, a trend really starts to reveal itself: The Eagles are getting killed down the seams (the area between the numbers and hashmarks). In fact, on passes to the seams, their completion percentage allowed rose in 2018 and is about the same this season (2017: 65.6%; 2018: 69.6%; 2019: 69.3%), despite passes traveling further downfield by a full yard each season (5.1 air yards per attempt in 2017, 6.1 in 2018 and 7.2 in 2019).

On passes down the seams traveling more than 10 air yards down the field this season, the Eagles have allowed 21 of 33 attempts to be completed for 416 yards, four TDs and one interception (134.2 passer rating, fifth-highest in NFL).

The source of the Eagles' pass-defense woes have been shots down the seams this season. As Steven Ruiz explored in this article last week, the biggest change in this secondary from its Super Bowl run to today has been its slot CB play. The base MOFC coverages of Schwartz's defense have been exploited by slot receivers and tight ends this season while actually performing well against outside WRs.

Patrick Robinson had a career year in 2017 as the Eagles' main slot CB (437 snaps aligned in slot, per Next Gen Stats), with the second-highest coverage grade (89.9) from PFF among slot CBs. Since then, the Eagles' slot CB position has been a revolving door, due to injuries and mediocre play. The three-headed monster of Cre'von LeBlanc (237 snaps, 66.1 coverage grade), Sidney Jones (174 snaps, 47.6 grade) and Dexter McDougle (93 snaps, 52.4 grade) failed to live up to Robinson's standards in 2018. This season, Avonte Maddox (102 snaps, 52.7 grade) has been mediocre as the main slot CB, with Orlando Scandrick (60 snaps, 64.3 grade) disappointing the Eagles' front office enough he was cut after the Week 7 loss to the Cowboys.

The Eagles' season is certainly still salvageable. After all, half the campaign remains, and they are only a half-game out of first place in the division. After beating the Bills on the road this week, they have three home games in a row, with a bye in Week 10, and four of their final five games are against teams with a combined 3-20 record. However, with the trade deadline looming this Tuesday, don't be surprised if general manager Howie Roseman makes a splash to fix their slot CB woes. As Ruiz mentions in his article, one of the best slot corners in the league -- Chris Harris Jr. -- happens to be on a team (the Broncos) that appears to be in the selling market. Upgrading the Eagles' slot coverage could be the key to getting this train back on track.

Follow Keegan Abdoo on Twitter @KeeganAbdoo.

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