by Derrik Klassen

There are not but a handful of defenses in the league as good or better than the Buffalo Bills. The Bills currently sit at fourth in defensive DVOA after having finished second only to the Chicago Bears in 2018. Though there may not be a true star in Buffalo's defense aside from cornerback Tre'Davious White, it is as sound a unit as any, and each individual fits perfectly within head coach Sean McDermott's system.

The Bills defense played winning football on Sunday. Tom Brady was held to a completion rate of 50% or worse for just the 21st time in 271 career starts, and the first time since 2017. The Patriots offense earned just 11 first downs after never earning fewer than 21 in the previous three weeks; they converted on just 5-of-18 (27.8%) third downs after converting 47.5% of the time in the first three games. New England also finished with by far their worst single-game offensive DVOA rating (-43.4%) of the year, having never dipped below 11.8% previously (subscription required). New England scored one offensive touchdown, with their other touchdown being a special teams score.

Buffalo's driving factor for success against the pass was good ol' Cover-1. Cover-1 is man coverage across the board with one deep centerfield defender and one free underneath defender who either blitzes, spies, or roams the middle of the field, depending on the exact call. McDermott primarily opted for "1 Rat" and "1 Cross" (at least that is what Nick Saban calls them). Without diving into either concept too much, it is fair to say both are versions of Cover-1 that ask a free underneath defender to roam over the middle as what many refer to as a "rat in the hole," hence the coverage title.

The idea in specifically playing "1 Rat" or "1 Cross" versus New England is to get any extra body in the way of Brady's prized middle-of-the-field throws within 10 yards of the line of scrimmage. Brady's ability to consistently find those routes, as well as Josh McDaniels' knack for scheming them open, is often the lifeblood for New England's passing game. Buffalo found a way to take it away without conceding much of anything elsewhere.

To make their coverages tougher to predict, Buffalo often loaded up at the line of scrimmage and dropped players back from there. Not only does doing so force the offense to respect a potential blitz, but it muddies which defenders will be dropping where, if they do drop back into coverage.

In this clip, safety Micah Hyde (23) walks down to the left side of the Patriots' formation after wide receiver Julian Edelman (11) motions across to the right side. Hyde stays tight to the formation and leans toward the line of scrimmage as if he might blitz, which would not be an unusual call from a defense rotating their safety away from the passing strength. At the snap, Hyde does not blitz; instead, he begins to backpedal with his attention turned toward the middle of the field. Hyde immediately finds Edelman trying to cut across the field and turns to play his inside shoulder while the slot cornerback plays from a trail position. Brady knows Edelman is completely blanketed and tries to loft a throw to wide receiver Phillip Dorsett on the outside, but cornerback Levi Wallace has him locked up to force the incompletion.

On other occasions, the Bills were more straightforward in their intent to play Cover-1. Typically, if a defense has one of their safeties rolled down toward the passing strength while their cornerbacks are in man coverage, they are going to ask that safety to cover the hash area. Buffalo did just that a number of times versus New England.

Again it is Hyde roaming the underneath area against Brady. This time, Hyde is playing over the right hash about 8 yards deep. Hyde initially falls for the run action, but does well to backtrack and float back up into the throwing lane between Brady and Edelman on the right side. Brady pulls the ball back for a moment as if he is going to throw to Edelman, but he sees Hyde in time and pulls the ball down. By the time Brady pulls it down and tries to look elsewhere, the Bills' front has swarmed around him and he is forced to throw it away in the direction of Dorsett.

In addition to a heavy dose of Cover-1, Buffalo made sure to take away with the middle of the field with a few other coverage concepts as well. McDermott knew all Brady and McDaniels wanted to do was open up the area between the numbers, but the defense-savvy head coach was not having it.

Before getting into the full play, take a look at New England's formation in the screenshot below. The Patriots are in a 3x1 set with trips to the field and a single receiver tight to the formation on the boundary side.

Tennessee Vols head coach Jeremy Pruitt (a Nick Saban coaching tree member) said in one of his coaching clinics that offenses will often tell you what they want to do. One of the tip-offs he mentioned was lining up a single receiver tight to the formation away from the field side, which is a sign that the offense wants to run a shallow crosser with that player because it is a good way to run them into space as quickly as possible. Furthermore, when offenses go into 3x1 sets like this and run a crosser from the weak side, they want to run at least one crosser the opposite way to create a mesh against the defense. The defense still has to have the discipline and talent to cover it, but New England is not exactly being discreet about what they want to do here.

And just like Pruitt foretold, New England ran a mesh concept with the two receivers tightest to the formation and another deep crosser with the No. 2 (middle) receiver to the trips side. Buffalo's answer was to drop the two linebackers they had peppering over the A-gaps (either side of the center) toward the field side and ask them to "wall" the middle of the field. By the time the defenders all match up, it ends up functioning sort of like Cover-1 -- every wide receiver is manned up, one safety is playing deep, and one man (Trent Murphy, who peeled off the line of scrimmage) acted as a roaming underneath defender.

This example is particularly interesting because of the "creeper" element. In short, the concept of "creepers" is when the defense loads the box with five or more defenders to show blitz, but drops a down lineman into coverage in exchange for bringing a second- or third-level defender. The idea is to throw the offensive line for a loop with regards to where the rush is coming from without actually having to bring a ton of pass-rushers. It would be unfair to do the entire concept justice in just a couple paragraphs, though, so read Steven Ruiz's piece on "creepers" for a more in-depth breakdown.

Of course, it took more than just flooding the middle of the field to beat Brady. The heavy serving of Cover-1 and similar concepts was a great call from McDermott, but at the end of the day, a lot of plays come down to how well players can execute one-on-one. This sentiment especially rings true down the field, where wins and losses come down to athleticism and skill, not just where a defensive coordinator put a player in position at the beginning of a snap. Buffalo's defense won their matchups down the field in a way few teams ever do against the Patriots.

Brady attempted nine passes beyond 10 yards versus the Bills. He completed just one of those passes, which was a wheel route to running back James White over linebacker Matt Milano that required perfect placement out of Brady. That pass was in the first quarter on New England's second drive of the game -- their only touchdown drive of the day. For the next three quarters and change, which consisted of 10 offensive drives, the Patriots did not complete a single pass beyond 10 yards or find the end zone.

There are a few reasons the Bills were able to pull off such a feat and there is plenty of praise to go around, but no player deserves more credit than cornerback Levi Wallace. An undrafted free agent in 2018, Wallace has quietly become one of the league's best cornerbacks and perhaps the best No. 2 cornerback (being that he plays across from White). He is a long, twitchy cornerback whose technique and savvy continue to impress.

Wallace shut down Dorsett, who had been massively productive for New England for the past few games. Dorsett is primarily a downfield threat, but Wallace never let him get open there. In the first three games of the season, Dorsett caught 13 passes on 14 targets with 14.4 yards per reception and three touchdowns. Wallace held Dorsett to just two catches in nine targets for a grand total of 10 yards.

Wallace shows off absurd quickness and technique in this clip. At the bottom of the screen, Dorsett initially opened to the sideline after a 10-yard vertical stem. Once Wallace turned his hips to the outside, however, Dorsett cut back up the field to continue vertically. Wallace executed a perfect speed turn to flip his hips back inside and close the gap on Dorsett. Though Wallace was trailing Dorsett for most of the play, he was playing him with an outside leverage and was distanced closely enough to tighten the window between himself and the deep safety. Brady did not really get a good window to throw into and subsequently threw an incompletion.

This time, Wallace is playing with a cushion and does not need to put himself in a trail position. Instead, Wallace plays over the top and remains patient while Dorsett gets through his route stem. Dorsett tries to give a little fake to the outside before shooting back up the field, but Wallace reads it all the way and stacks over the top of Dorsett the moment he declares vertically. Wallace severely impedes Dorsett's pace down the field while never getting physical enough with him to draw a penalty. Though Wallace trips over himself at the end of the play, he had already done his job and killed the throw before it ever had a chance.

What often follows performances like this against Brady is a barrage of takes about how this is the new way to shut down the seemingly unkillable quarterback. And yes, playing near-flawless Cover-1 with high-end cornerbacks is, in fact, a great way to beat Brady. The reality is that only a small handful of other teams have the talent and elite defensive coaching to pull it off, and even those who do are never guaranteed to pull off the feat.

In turn, Buffalo's defense should not be looked at as a blueprint for how to beat Brady. If, say, the Jets or Giants try to do what the Bills did on Sunday, they will get the breaks beat off of them while Brady chuckles his way to 400 yards passing. Instead, it is better to simply appreciate Buffalo for what they were able to accomplish against a timeless tyrant and get excited for what they may be able to do to other top quarterbacks as the season rolls on. The Bills' quarterback situation likely puts a cap on the team's overall quality, but as far as defense goes, there are not many doing it better than McDermott's squad.