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Over the last few years, the Green Bay Packers were repeatedly let down by their defense. Under former defensive coordinator Mike Pettine, the Packers couldn't break out of the realm of "slightly below average" on the less glamorous side of the ball, and after a disappointing showing in the NFC title game for the second consecutive season, the Packers decided to make a change. 

Green Bay brought in Joe Barry, the former linebackers coach and assistant head coach of the Los Angeles Rams, to run the defense. The Packers have gotten the results they wanted. Despite playing most of the season without their two best players (Jaire Alexander and Za'Darius Smith), the Packers' defense ranks above average across the board. They're inside the top 10 in yards and points allowed per game, and in the top half of the league in yards per play, points per drive, EPA per play, and Football Outsiders' DVOA. They've also forced a turnover on the eighth-highest share of opponent drives and allowed a touchdown or field goal on the eighth-lowest share of drives. 

YearYds/GmPts/GmYds/PlayPts/DriveEPA/PlayDVOA
2018182214232129
201918922111415
202091317171817
20217511151414

A pertinent question, then, is how have they done it? Barry spent last season working under then-Rams defensive coordinator (and now head coach of the Chargers) Brandon Staley, and the previous few years before that working under one of the best defensive coordinators of all time in Wade Phillips. Earlier in his career, Barry worked under both Monte Kiffin and Rod Marinelli (who is also Barry's father-in-law). Those are four fantastic defensive minds from whom to learn, and Barry has done an admirable job of marrying concepts from each of them in coaching this Green Bay defense. 

From Staley, Barry has brought along the idea of prioritizing stopping the pass rather than the run. Green Bay plays with a light box (i.e. six or fewer defenders close to the line of scrimmage) more often than not, encouraging opponents to run the ball by taking away their pass options deep down the field. 

Despite those alignments, the Packers have been able to play the run decently well. Only two teams (the Rams and Chargers, naturally) have faced more opponent rushing attempts with six or fewer defenders in the box, per Tru Media. The Packers have been basically an average run defense on those plays. That's all you want to get out of that type of alignment. If you're just as good at playing the run as other teams that devote an extra player to defending it, you gain an extra pass defender with little cost to your defense. 

Like Phillips, Barry has shown an ability to get his best players isolated in space, where they are able to take advantage of matchups and create splash plays. Even in the absence of Za'Darius Smith, Rashan Gary has faced double-teams at a significantly lower rate than the average edge rusher, according to tracking data obtained by ESPN. Gary has taken advantage of that fact and racked up 44 pressures, the 13th-most in the NFL, as well as 6.5 sacks. 

Kenny Clark has been a monster up the middle, putting together arguably the best pass-rushing season of his career. Clark already has 40 pressures this year, tied for 17th-most in the NFL. Clark doesn't play straight up nose tackle as often now as he used to (he's lining up on the outside shoulder of the guard this year, more often than he's at the nose), and being able to slice through gaps rather than always being counted on to occupy two of them has freed him to get after it in the backfield a bit more often. 

One thing you might notice about each of the plays in the Gary and Clark clips above is that the Packers are lined up in four-man fronts. Those fronts mostly include two down linemen on the interior and two stand-up rushers lined up out wide. They'll creep a linebacker up toward the line of scrimmage behind that front as well, both to take away a gap in the run game and force adjustments in pass protection. 

Playing that way up front allows Barry to utilize two-high safety shells with regularity. But the Packers don't just stay in a regular two-high coverage. In fact, out of the 451 passing snaps they've faced, they have played only 20 total snaps in Cover-2 or 2-Man, or according to Tru Media. 

Instead, they are spinning into some other coverage more often than not. Green Bay has played Cover-3 (a single-high safety coverage) more often than anything else, utilizing that look on 31.7 percent of opponent passing snaps. They've gone to Cover-4 19.5 percent of the time, and Cover-6 on 18 percent of snaps. That's a lot of variability, and among coverages that all fit together to take away the types of plays that one or the other is vulnerable to. 

Cover-6, for example, is a combination coverage wherein the defense plays Cover-2 to one side of the field and Cover-4 to the other. (4 + 2 = 6, duh.) Rotating to that out of a two-high shell can be confusing because quarterbacks may not know which player is responsible for which deep zone, and who is rotating over to the hook/curl zones or into the flat. (The graphic below just shows a standard Cover-6 rotation. There are other ways to get into it.) 

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Cover-6 = Cover-4 to one side, Cover-2 to the other

They've taken advantage of, among others, Matthew Stafford and Russell Wilson with this coverage, coming away with interceptions because a pass the quarterback expected to be open wasn't, and he ended up forcing a throw into directly into coverage. 

It helps that the team's cornerbacks (even without Alexander) are playing really well. Prior to his injury, Alexander was averaging 1.02 yards allowed per coverage snap, according to Tru Media. In his absence, Rasul Douglas is at 1.04 per snap, Chandon Sullivan is at 1.09 per snap, and rookie Eric Stokes is at 1.16 per snap. If passer rating is more your speed, consider that Douglas has allowed a 51.0 rating on throws into his coverage, Stokes has allowed 63.2, and Sullivan has allowed just 73.9.

Having Adrian Amos and Darnell Savage provide help over the top surely has something to do with that, as does the terrific play of linebackers Krys Barnes and (especially) De'Vondre Campbell. When you play a lot of zone coverage, those are the players mostly responsible for the middle of the field, where throws are more likely to go because opponents will search for the soft spots in between zone defenders. Getting high level play from your safeties and linebackers is key to executing the kinds of defenses Green Bay utilizes, and that's exactly what the Packers have gotten. 

It remains to be seen how the Packers will deal with an opponent that decides to simply run the ball down their throats all game long -- the type of opponent that gave them issues during the Pettine era. The offense staking them to leads throughout the season has taken that option off the table in many games, but so has the defense's own performance in running situations. For those reasons, it looks like a team better set up to defend the best offenses this year than in years past -- especially if and when they get their two Pro Bowl defenders back on the field.