Just last season, the Buffalo Bills' pass defense was one of the big reasons they were able to snap a 17-year playoff drought.
In 2017, the Bills allowed a relatively high 64.6 completion percentage to opposing quarterbacks (eighth highest allowed by a defense), but they were great at bending without breaking, limiting opposing offenses to just 6.7 yards per pass attempt (ninth) and coming down with 18 interceptions (sixth).
In terms of Pro Football Focus grades, the Bills pass defense graded out as the sixth-best coverage unit in the NFL, collectively earning a 91.2 grade, a grade in which we consider elite.
Through two games in 2018, nobody is calling Buffalo’s pass defense elite.
So far this season the Bills have allowed a 75.4 completion percentage to opposing quarterbacks (second worst in the league); they rank 22nd among defenses by allowing 7.9 yards per attempt and they are one of four teams without an interception.
As a unit, the Bills' defense has a 56.0 coverage grade, the seventh-lowest among all NFL teams.
Buffalo’s pass defense has gone from strength to weakness – at least initially to start this season – which begs the question, how?
The Bills were a zone-heavy team with Sean McDermott’s arrival in 2017, running zone coverage on 65 percent of opponents’ passing attempts. They’ve taken that to an entirely new level, running some form of zone coverage on 90.4 percent of opponents’ passing attempts through two games.
Looking at the 2017 coverage data we collect at PFF, they might want to consider getting back to mixing in man coverages with more regularity.
When playing man coverage in 2017, the Bills' defense allowed a 54.2 completion percentage while surrendering 6.3 yards per attempt. They also had a contested target rate of 29.9 percent when in man coverage – we define a contested target as one where the coverage defender contacts the ball, the targeted receiver or he compresses the catch point before the receiver secures the pass.
In zone coverage last season, they allowed a 68.4 completion percentage, 7.4 yards per attempt and they only contested 10.7 percent of their opponents’ targets.
Simply put, the Bills were tougher to pass on last season when they were in man coverage, and they’ve played very little of it so far in 2018.
Looking beyond coverage schemes, one of the specific areas that has given the pass defense troubles this season is covering play action. Buffalo graded out as the third-best coverage unit against play action in 2017 at a 73.1 grade, but their grade against play action so far sits at just 58.5, dropping them to 16th.
A season ago, the Bills allowed just 7.0 yards per attempt off play-action passes, the fourth-lowest rate surrendered by any defense, and opposing quarterbacks had just a 90.2 passer rating when throwing off play action, the sixth-lowest rating allowed and nearly 15.0 points lower than the league average of 105.0.
Buffalo has surrendered 8.9 yards per attempt off play-action passes this season to go with a 139.7 passer rating allowed off such throws. The Baltimore Ravens and Los Angeles Chargers combined to pick up either a first down or touchdown on 60 percent of their pass attempts off play action in Weeks 1 and 2. For comparison, last season the Bills surrendered either a first down or touchdown on just 35.7 percent of the play-action pass attempts against them.
Looking at PFF grades to assess individual performances within the Bills passing defense also makes it glaringly obvious that this is a unit that hasn’t lived up to what it showed in 2017.
The Buffalo secondary had three players last season earn elite coverage grades (over 90.0) with Jordan Poyer (90.7), Micah Hyde (90.3) and Tre’Davious White (90.1). In addition to those three, they also had EJ Gaines who earned an 86.4 coverage grade.
Through two games, Poyer’s coverage grade sits at 64.0, while Hyde and White have earned grades of 65.1 and 68.6, respectively, and they’ve struggled to find a replacement for Gaines.
The Bills also replaced Preston Brown with Tremaine Edmunds, and while Brown was no stalwart in coverage (earning a 58.3 coverage grade in 2017), Edmunds has really struggled to cover so far as he adapts to the NFL, posting just a 27.8 coverage grade.
The Bills need their stars to play like stars. They need to tighten up against play action and they should consider playing more man coverages based off the success they had with them one season ago.
There are undoubtedly additional contributing factors to the woes they’ve had so far this season in pass defense, but those are three areas that have seen a major change when comparing the 2017 team to the current one.