This is Cover 3.

It’s the primary coverage that Jim Schwartz runs when coordinating a defense. There are a few reasons why.

Because Cover 3 is a single-high coverage, you can rotate your strong safety down into the box as an extra run defender (SS in above diagram). This gives you a numbers advantage in the box, making it difficult for the offense to run the football. This point is especially important because... Cover 3 needs a powerful four-man rush, which we know is what Schwartz likes to do with his defenses. With an extra defender in the box, you can really let your rushers tee off without worrying about the run; they have help on the way. By moving a safety up into the box (namely: Malcolm Jenkins) and playing a true single-high shell, a defense can be more immediate and direct in bumping tight ends as they enter the seams, which is a weak point in the Cover 3 defense. By delaying those releases, you create more time for the pass rush to arrive.

On downs in which the run is a legitimate possibility, Jim Schwartz likes to line up pre-snap with a single-high safety, so as to be +1 in the box. Let’s acknowledge that as our hard and fast rule for the Schwartz defense: single-high safety, +1 in the box, at the snap.

Now, if you play exclusively Cover 3, you’re going to lose football games, because everyone knows what you’re doing, all of the time. Even the Cover 3 Kings — the 2013-2014 Seattle Seahawks, with Richard Sherman and Earl Thomas and Kam Chancellor — needed to vary their coverages, and even use different styles of Cover 3, to keep things fresh.

And Schwartz has been doing the same: varying the post-snap coverage that follows his pre-snap single-high look, in an effort to stay unpredictable and capitalize on offensive assumptions.

In that spirit he has introduced, to a much greater degree this season, what can be called “Inverted Cover 2,” “Cover 3 Robber,” or how I understand it, “Tampa 2 Robber.” It’s essentially a trap coverage out of a Cover 3 shell, and it was paying off for Philadelphia early in the season. This from Week 1:

Rodney McLeod (highlighted pre-snap) doesn’t reel in this football, but this is a turnover-worthy play generated by the coverage call.

With a hi-lo stretch on the curl defender to the strong side of the field (curl underneath, in over the top), this is Cover 3 beating play. The expectation is the WR Calvin Ridley (targeted) will cut into the intermediate space behind the linebackers, in front of the Cover 3 corner and deep safety. He’ll be open for easy yardage.

But because Rodney McLeod did not enter the deep Cover 3 zone, but rather stayed in the zone area of the field we would call the hole zone — “hole” in that it’s typically wide open. On the chalkboard, this is an beautiful interception created by defensive play-calling.

I call the coverage the Eagles ran on this play Tampa 2 Robber — and I’d argue that’s the best name for it — because of the unique responsibilities of that hole defender. To understand his responsibilities, we can turn to the original Tampa 2 defense: a coverage of the early 2000s popularized by Tony Dungy’s Tampa Bay Buccaneers and Lovie Smith’s Chicago Bears with Brian Urlacher.

The Tampa 2 defense was a mutation of the common Cover 2 defense. Tampa 2 came to be because it addressed the primary weakness of the coverage: the “hole” zone, the vacant space in the middle of the field between the two dropping safeties and three underneath linebackers.

Cover 2 asks the middle linebacker of the defense to cover the hook zone, as you see pictured above. Typically about 12 yards deep, the middle ‘backer handles intermediate crossers and any in-breaking routes from slot receivers or tight ends. But if you put a crossing route in front of that linebacker, and then send a player behind him — say, an athletic tight end like Antonio Gates or Tony Gonzalez (remember, this is the 2000s) — the safeties won’t be in position to close on that tight end, while the middle linebacker will be focused on the route in front of him.

Easy money.

So Dungy adjusted by sending the middle linebacker deep down the field, asking him to carry any vertical stems that came through his zone. He essentially remained a hook defender, but played the hook from a deeper alignment, and could change into a hole defender if the offense was looking to attack the hole.

This is an explanation of the Tampa 2 from Ross Tucker when he was with the Eagles’ team site. The Eagles are prepping for a game against St. Louis, as Jeff Fisher’s Rams were still playing Tampa 2 in 2015, God bless his soul.

There’s a really important quote here from Ross; one that we need to wrap our heads around if we’re to understand what’s going on with the Eagles’ defense:

Typically the weakness in the Cover 2 is the middle of the field, but because the middle linebacker runs with anybody that goes down the middle of the field, it actually in effect becomes a Cover 3 on the back end, and that helps the defense not be exposed by anything vertically down the middle of the field.

The Tampa 2 is indeed a three-deep coverage, once that middle linebacker gets into the hole zone. This is why you’ll see, in the original diagram we posted of Cover 3, that the underneath defenders have hook/curl and curl/flat responsibilities. It’s because each defender is essentially responsible for two zones — the hook first and then the curl (or the curl first and then the flat), depending on which routes come in to which zones.

The underneath defenders have to play through multiple zones because they’ve lost a body to account for an underneath zone. That body is the middle linebacker, who is now playing a deep zone.

Three deep; four underneath. Tampa 2 is Cover 3, just with different players executing the responsibilities therein.

Philadelphia’s Tampa 2 Robber is easily identified as a three deep, four underneath coverage — it’s Cover 3. But, just like the three-deep responsibilities of the Tampa 2 are slightly twisted, so are the responsibilities of the Tampa 2 Robber.

Instead of sending the middle linebacker back into the hole zone, the Tampa 2 Robber asks the deep safety to come forward at the snap to enter the hole zone. Across all coverages, the “Robber” terminology refers to the action of a deep safety coming downhill at the snap — an atypical occurrence — to enter that hole zone.

The underneath defenders continue to play their hook/curl and curl/flat responsibilities as they would in any old Cover 3, while the cornerbacks bail heavily at the snap. The corners align themselves on the numbers, playing with outside leverage and their eyes on the routes developing all across the field. The hole safety reads the quarterback’s eyes and looks to jump underneath any in-breaking routes, as McLeod does in the clip against Atlanta.

The Tampa 2 Robber was such a nice change-up to the vanilla Cover 3 looks of Philadelphia that I wrote a post — back when McLeod was still healthy, mind you — advocating for a couple of things, including an increased usage of Tampa 2 Robber.

And now we turn to the Tennessee tape, wondering how the Eagles defense was gashed on so many deep balls.

The answer is the heavy reliance on the Tampa 2 Robber coverage, which Jim Schwarz leaned on heavily against the Titans. It was his first game without Rodney McLeod, who the Eagles lost to injury during the Colts game. With Corey Graham as his backup safety, Schwartz clearly didn’t think he had a player with sufficient range to play centerfield — the deep zone traditional of Cover 3 free safeties — and still affect throws to the boundary.

So he flipped to Tampa 2 Robber as his base coverage. And the Titans attacked the weaknesses accordingly.

In that the free safety now accounts first for the hole zone in Tampa 2 Robber, the deep middle of the field is vulnerable. That’s why you see the cornerbacks — Jalen Mills and Ronald Darby — bailing hard at the snap. They need to get depth down the field in case the offense is attacking that deep zone. Consequentially, the flat defenders bail hard into their flat zones, in case the offense wants to attack those shallow areas that the boundary cornerbacks are vacating.

We see Ronald Darby (bottom of the screen) get a huge deep cushion at the snap, while Jalen Mills (top) stays in for a moment to process the run action to his side of the field. Once play-action is diagnosed by the defense, you can see the flat defenders turn and run to the shallow areas, while Avonte Maddox — the deep safety at the snap — comes downfield to account for the tight end coming up the seam.

As Jalen Mills identifies that there are no immediate threats to his deep zone, he appropriately adjusts or overlaps his deep zone to help Ronald Darby. Darby has to retain outside leverage against his receiver, but again, that deep middle has been vacated by the hole defender. So Mills — you can see him waving his arm — notifies the secondary that he is bailing to that deep area of the field. Nobody is threatening his deep third, so he’s coming over to help Ronald Darby.

Marcus Mariota looks for that deep route — this is the first play of overtime, and the Titans have hit on a similar route multiple times today — but because Mills has overlapped coverage underneath the route, there’s nothing doing.

As evidenced here, the cornerbacks in Tampa 2 Robber have responsibilities that extend beyond those of the typical Cover 3 zones. When a deep crossing route attacks a boundary corner in Cover 3, they typically have safety help in the middle of the field — but in Tampa 2 Robber, that help isn’t always there. So the opposite corner has to be privy to potential downfield crossers, while the active corner must be more urgent when getting connected to in-breaking routes.

This is where Philadelphia’s defense really struggled against the Titans — both Jalen Mills and Ronald Darby, though Darby had the rougher day.

This is the shot play that started the go-ahead drive for the Titans late in the fourth quarter. It’s essentially a Yankee concept — two-man route pairing, with an intermediate crosser and a deep crosser. Notice how both the intermediate and deep crossers give little double move/vertical fakes in their routes before eventually breaking across the field.

That’s really, really pretty.

The Kyle Shanahan system, from which Titans OC Matt LaFleur’s playbook originates, is full of Yankee concept plays — but it’s also full of plays that look like Yankee, then suddenly break off into something else. The deep stems of Yankee put the Cover 3 corners on islands — even bigger islands than usual, because Mills and Darby here both have the extended Tampa 2 responsibilities we discussed.

Those corners did film study — they know LaFleur will fake Yankee and run something else. So they’re really dealing with a lot mentally, and LaFleur knows that. The Eagles have been running this Tampa 2 Robber all game, and this double bluff Yankee concept puts a huge cognitive load on the corners. That’s just great coordinating.

The vertical fake by Corey Davis (targeted) does enough to widen Jalen Mills back to the sideline, which gives him a clear shot to the middle of the field. Ronald Darby could be there to overlap that deep crosser, taking on some of that deep middle responsibility — but he fails to do so, even though his primary deep threat (the intermediate crosser) vacates. He isn’t there to help Mills, who is tasked with tracking a 4.4 player — to whom he rightfully gave up inside leverage — across the deep middle of the field.

The onus on the boundary cornerbacks in Tampa 2 Robber is too great to run it as a base coverage. Again, on a deep shot to Corey Davis on a crossing route — this from the first drive of the game — Mills is tasked with chasing down a superior athlete. This time, Darby didn’t so much fail to adjust his zone as he was occupied by the play design of Matt LaFleur.

This play is built to beat Cover 3 — and because Tampa 2 Robber is still just Cover 3, the Flood concept still wins. LaFleur uses the flat route from the running back to occupy the flat defender; the deep comeback to occupy the deep cornerback; and he expects the intermediate crosser from the tight end to open up.

But because the Tampa 2 Robber hole safety attacks the intermediate crosser instead of bailing deep to account for the deep crosser, the deep crosser opens up. Jalen Mills is expecting help from Ronald Darby again on this play, but because there’s a deep comeback route in Darby’s zone, he’s unavailable.

Mills caught a lot of flak from some analysts for seemingly jogging this route out, but because he thinks that deep half is covered, he’s really just maintaining his leverage. As we see in the later plays, Mills is much quicker to get on his horse against these crossers — as we said above, Tampa 2 Robber corners must be urgent to get connected to crossing routes, because that deep middle help might not be there.

A final point on Tampa 2 Robber: you’ll notice that all three of Tennessee’s big plays against this shell come off of play-action passes. And the logical train isn’t hard to follow: Because the linebackers have that hole defender behind them, they are free to play very hard into the line of scrimmage when they read run action. The vacuum they create sucks in that hole defender, as he takes the first crosser that flashes — and now you’re basically left with two cornerbacks, playing Cover 2 zones, against receivers with free downfield releases. (In typical Cover 2, corners at the line of scrimmage jam to force inside releases, which helps those Cover 2 safeties.)

That’s a huge win for an offense, and Tennessee exposed that.

While the theory behind wrinkling Tampa 2 Robber in with Cover 3 is sound, Tampa 2 Robber is not a primary coverage and cannot be used as such — like all trap coverages, it has too many weaknesses. Philadelphia needs to figure out who they can trust as that Cover 3 free safety if they intend to continue using their three-deep shells as their base coverages.