The turnovers were great for Dallas, but were they worth the yards?
Trevon Diggs has become a hot topic of conversation in the football community. Some believe that Diggs surrendered too many yards in 2021 and ultimately hurt the Cowboys. The other faction believes the All-Pro and Pro Bowl selections were justified for the second-year corner due to his big-play ability.
Luckily for us, there are methods for quantifying interceptions. And in doing so, we can determine:
- Did Diggs’ interceptions make up for the yardage allowed?
- How does Diggs compare against the other NFL corners when taking into account interceptions?
Determining the value of Trevon Diggs’ eleven interceptions
Interceptions and yards allowed
Were the 1,016 yards allowed worth the eleven interceptions? That is the question that seems to exist every time the name Trevon Diggs is mentioned. In the comments section of social media posts, next to the watercooler at work, and even within most Dallas Cowboys fans’ minds, the question remains. It is difficult to evaluate such a spectacular, but peculiar, season.
In 1988, The Hidden Game of Football estimated that an interception is worth 45 yards. This is not only due to the fact a turnover stops the opponent from gaining additional yards on the drive, but they are not able to punt. The net punting average in the league is over 40 yards. Meaning that an interception prevents the opponent from scoring and prevents them from flipping the field.
To use Diggs as an example, his interception against Taylor Heinicke was not worth practically anything since it was 45 yards downfield. However, his pick-sixes against the Eagles and Patriots were worth a heckuva lot more than 45 yards. So, keep in mind it is an average instead of a number that applies to any situation.
Now, in 2003, Football Outsiders updated the number to be worth 55 yards plus the return yards. As offenses score more points, the value of an interception increases. A turnover is likely worth more than 55 yards (+ return yards) in 2021, but let’s stick with this number.
Here is how that looks with Trevon Diggs’ 2021 season:
- Yardage allowed: 1,016
- Interception value: 605 yards (55*11)
- Return yards: 142 (per Pro Football Reference)
- Adjusted Total Yardage Allowed: 269
So, yes Diggs gave up a lot of yards in 2021. But when you consider the value of his eleven interceptions, the yardage was close to worth it. Regardless, the above number is positive. This implies that the interceptions were not advantageous given the yardage surrendered. However, how does this compare against the rest of the NFL?
The NFL’s best CBs when adjusting for interceptions
As a quick preface, there are other ways to evaluate the totality of an NFL cornerback’s season. For example, EPA per play allowed is a great indication of how the cornerback added (or subtracted) points to the opposing offense. Along with a few names you will see later, Diggs’ 2021 campaign looked like:
- Diggs: -11.88 (lower is good)
- J.C. Jackson: -11.70
- Rasul Douglas: 5.53
- A.J. Terrell: 29.07
Based on EPA per play allowed, no cornerback is better than Diggs based on the targets he saw. However, EPA tends to view turnovers as disastrous for the offense and amazing for the defense. This is not to say the metric is wrong, turnovers are game-changing plays. But it does play well into Diggs’ 2021 season.
Instead, what if we rank cornerbacks based on the yardage measure we used for Diggs (yards allowed – 55 yards for each int plus the return). Stopping the opposing offense from gaining yards and forcing them into making mistakes are the two biggest jobs a defensive back is responsible for. Just as any other metric, this is not a perfect representation of cornerbacking ability. But it does measure yardage allowed versus the benefit of interceptions, which is at the heart of the Trevon Diggs debate.
We will offer two different rankings. The first is yardage on a per-target basis. Trevon Diggs’ 96 targets versus Richard Sherman’s 15 targets should not be considered equal. Here is the adjusted yardage allowed based on interceptions on a per-target basis:
- Rasul Douglas (GB): -.17
- A.J. Terrell (ATL): -.06
- J.C. Jackson (NE): .93
- Amani Oruwariye (DET): 2.52
- Trevon Diggs (DAL): 2.80
And then there is the argument that, although Diggs was targeted a lot, he was baiting the defense into it. He wanted to be targeted for the high-upside potential of an interception. Per target might not properly reward the cornerbacks who play consistent lockdown defense and do not see any yards. So instead, here is the adjusted yardage on a per-snap basis:
- Rasul Douglas (GB): -.02
- A.J. Terrell (ATL): -.01
- J.C. Jackson (NE): .16
- Amani Oruwariye (DET): .33
- Trevon Diggs (DAL), Denzel Ward (CLE), D.J. Reed (SEA): .41
Diggs had the seventh most snaps in coverage among cornerbacks in 2021. The rankings do not change on a per-snap basis with the exception of two solid cornerbacks joining Diggs to tie for the fifth spot.
In case you were wondering where Anthony Brown and Jourdan Lewis finished by this metric (per-target ranking/per-snap ranking):
- Anthony Brown: 33/55
- Jourdan Lewis: 36/42
This is among the 99 cornerbacks who played more than 250 snaps in 2021. So by this specific metric alone, Brown and Lewis are completely competent at what they do. In fact, among the starters, they are above average.
But what did we learn about Trevon Diggs?
- The yards that Diggs allowed do matter. The second-year cornerback was not the best in the NFL last year despite his eleven interceptions because he did allow a decent chunk of yards.
- Inversely, to suggest that Diggs was not a top-five cornerback in the NFL last year is a little misguided. Not only did he finish with the best EPA per play among cornerbacks but when you adjust for the interceptions, he was top five in yards allowed, both per snap and per target. The 1,016 does not automatically make him a bad cornerback.
2022 is worth discussing. The purpose of this article is only to review 2021 performance in light of the yardage allowed vs. eleven interceptions debate. This is not an argument that next season Diggs will be horrible if he doesn’t hit double-digit picks. This isn’t even an argument that he is a top-five CB heading into next year. This is only a revisionist analysis, there are no projections here.
No one knows what will happen in the upcoming season. What if the interceptions don’t come? Will Diggs allow fewer yards and play tighter? Will he continue to surrender receptions? Only time will tell. But for now, the argument that Diggs is mediocre or below average because of the yards he gave up is proven incorrect. He was a good (not the best) CB last year. And it was sure fun to watch.