The Short Shadows of Cover Corners
After close to two decades as Tom Brady's playground, the AFC East needs a new identity. Brady's direct replacement Cam Newton offers one option since he and new division rival Josh Allen are cut from the same cloth of power-running quarterbacks, but I'll propose a brand with its own extended history in the division. Dating back to Darrelle Revis' prime at the turn of the last decade, the division has frequently been the home of some of the game's best cover cornerbacks. That was true in 2019 and should be true again in 2020 with reigning Defensive Player of the Year Stephon Gilmore of the Patriots, as well as Tre'Davious White of the Bills. Even with their routine assignments against their opponents' best receivers, Gilmore and White both finished in the top 20 of 89 qualified corners with respective 6.4 and 5.9 yards allowed per target, and they were the biggest reasons their teams finished in the top five in pass defense DVOA last season.
Revis Island introduced many fantasy fans to the idea of playing coverage matchups, and after his recent accolades, Gilmore may spark a renewed conversation about the strategy. I think he should. With the advent of daily fantasy, matchup considerations have never been more important than they are today. But coverage matchups are more difficult to play than many more common matchup factors because different cornerbacks have different tendencies in the types of players they cover and how frequently they stick to a single receiver's hips.
Again, this is a situation where fantasy managers with 15-plus years in the game have a leg up. The managers who recognized Revis' effect on their teams' receivers likely tried to apply what they learned to their matchups with one of the game's other best corners of that era, Nnamdi Asomugha of the Raiders. But if they tried that, they soon discovered that Asomugha stuck to the right side of the field. That approach likely helped him excel because of the expertise he developed in a specialized role, but it also allowed those benched fantasy receivers to rack up points by simply moving to the other side of the formation to draw better assignments.
Gilmore and White are more of the Revis mold of shutdown corners, and their teams have other impact pass defenders. You probably won't make too many mistakes if you err on the side of pessimism when your fantasy players face the Patriots and Bills this season. But the salary setters on daily fantasy sites know that too. And if you want to identify values based on coverage matchups, you have to learn how shutdown corners can have uneven effects on their opponents' receivers, even if their defenses are broadly speaking some of the best in football against the pass.
The Patriots teased that truth in the variance of Gilmore's shadow coverage rates of their opponents' most-targeted receivers entering their matchups. Gilmore stuck to the hips of six of his opponents' presumed top receiving threats, covering them on at least two-thirds of their targets. And he shut down all but one of those players, holding Odell Beckham, Tyler Boyd, John Brown, and Amari Cooper to 10 or more yards less than their projected totals before defensive adjustments.
|Top-Targeted Wide Receivers vs. Patriots, 2019|
|Shadow% reflects target rate with Stephon Gilmore in coverage.
Projections adjusted for venue and weather but not defense.
However, the Patriots enjoyed similar success against the receivers that Gilmore never or rarely defended. Tyreek Hill, Jamison Crowder, Nelson Agholor, and DeVante Parker (in Week 2) saw similar yardage shortfalls. The first three never saw Gilmore as a primary defender, and Parker saw him on just one of his seven targets that week. It turns out that J.C. Jackson and Jason McCourty are really good, too. They actually beat Gilmore with 4.0 (first) and 5.1 (eighth) respective yards allowed per target last season, albeit typically against less talented receivers or -- in the case of slot players such as Crowder, Agholor, and Golden Tate -- receivers who ran shorter routes.
By rank, the Bills (fifth) were not far behind the Patriots (first) in pass defense efficiency. But the differences they showed between the receivers that White covered and those he didn't illustrate how special the Patriots defense was last season.
|Top-Targeted Wide Receivers vs. Bills, 2019|
|Shadow% reflects target rate with Tre'Davious White in coverage.
Projections adjusted for venue and weather but not defense.
White held three of the four receivers he shadowed on two-thirds of their targets to 10 or more yards less than their defense-unadjusted projections. (Late-season Parker was the exception like he was against Gilmore -- jump on him at his fifth-round ADP.) But the receivers White did not shadow -- such as Crowder, Julian Edelman, and Preston Williams -- all exceeded their yardage expectations. That's because the Bills did not have the same depth at corner that the Patriots did. Their second option at the position, Levi Wallace, allowed 7.0 yards per pass, just 31st at the position. And that sort of coverage inequity -- which more often than not exists on teams with the best shutdown corners -- can act as a lever to shift opponents' targets away from their typical top receivers to their second and third receiving options. Wallace himself saw 26.5% of his opponents' targets, the third-highest rate of qualified corners in football.
The Bills -- and by similar logic many other teams with one shutdown corner and lesser talent behind them, such as the Ravens and Chiefs -- can be an OK matchup for your fantasy receivers. But you need to know whether those receivers are likely to draw White (or whichever shutdown corner) in shadow coverage. That's an undertaking that can require a lot of homework. Our weekly projections and, in aggregate, KUBIAK projections aim to make it easier by segmenting defensive performance against types of receivers rather than each individual receiver's assumed coverage assignments and shadow percentages.
I made a few references to defense factors in my previous article about the Panthers' bad run defense. And even though that piece argued that overall team quality was a better predictor of good and bad rushing matchups, our projections use team efficiencies of catches, yards, and touchdowns per attempt and target to make most of their defensive adjustments.
Those defense factors work like park factors do in baseball analysis and are applied in a similar fashion. A neutral factor is displayed as 100.0, and each count above or below 100.0 represents a percent of expected gain or loss of its metric relative to an average team. From the perspective of your offensive fantasy players, defense factors above 100.0 should add extra fantasy points relative to a neutral matchup. And as you would expect given their quality of pass defense DVOA rates, the Patriots and Bills had the lowest overall yards-per-target factors as of the end of last season.
Still, note the differences of their receiver-type splits. Gilmore and White drove similar reductions in the yardage gains of their opponents' No. 1 receivers, but the Bills had a lesser impact (83.0 vs. 70.3) on their opponents' secondary receivers. And while the Patriots (36.0) and Bills (31.7) were both nails against deep threats, they were palatably poor matchups (89.6 and 84.0) for slot receivers. With some of the league's best coverage linebackers in Devin Bush (6.0 yards allowed per target), Mark Barron (5.7), and Roquan Smith (5.5), the Steelers (35.9) and Bears (44.9) were the defenses to avoid for those receivers.
Football has a sample-size problem, and that problem is magnified the more you partition its play-level data by things like types of receivers. We combat that issue with regression to league averages, especially at the starts of seasons when teams see their biggest game-over-game changes in defensive personnel and even consistent players see big changes in quality of play. Still, even the subtle matchup gains and losses we apply to different types of receivers can be hugely different than those that work from a catch-all approach to defensive adjustments. The 2019 Patriots had the talent and depth to hurt the production of pretty much every receiver they faced, but most teams do not, and even the best of those in overall pass defense can be plus matchups for the receivers who can target their specific weaknesses.