What Impact Does a Dominant Secondary Have on an NFL Team's Overall Success?

The New York Jets have doled out some major moola to defensive backs this free agency period. Does that mean they can push for the playoffs without offensive improvement?

In the Caribbean Sea, east of Puerto Rico, sits the island nation of Anguilla. The people seceded from British rule in 1971, forming a separate British dependency.

The economy of Anguilla depends largely on tourism, banking and lobster fishing. These factors combine to give this quaint, picturesque country a gross domestic product of $175.4 million.

That is also roughly the amount of money the New York Jets have spent on their secondary the past four days. God bless America.

In signing four new defensive backs via free agency, new general manager Mike Maccagnan has recognized how bad the team's pass defense situation was last year. He had cap space to use, and he did so in a big way on the secondary.

The question now becomes what effect a top-notch secondary can have on a team's overall success. The Jets' offense is still a huge question mark, even after the acquisitions of Brandon Marshall and Ryan Fitzpatrick. Can a great secondary overcome a below-average offense?

We'll attempt to answer this using numberFire's Net Expected Points (NEP) metric. If you're new to numberFire, NEP measures how a team performs relative to expectation. There are an expected number of points a team will score on a drive in each situation. If they get three yards on 4th-and-1, for instance, that'll have a larger NEP impact than a three-yard gain on 4th-and-4, whereas a simple yards-per-play measure would mark the two events as equal. You can read more about NEP in our glossary.

For this specific study, we'll be looking at Adjusted NEP per play. This is adjusted based on strength of opponents and scaled down to a per-play basis.

So, can the Jets overcome their potential offensive ineptitude by throwing fat stacks at d-backs? Let's find out.

It's a Passing League

In order to investigate the effect a secondary has on a team's overall success, I looked at the NEP numbers from teams over the past five seasons. I took their Adjusted Passing NEP per play and Adjusted Rushing NEP per play along with those two categories on the defensive side of the ball. I then found the win total associated with each team to see how each of the four statistics correlated with the team's win total.

Obviously, this is not the greatest way of doing this. It would be best if I could do some sort of regression analysis to isolate various elements. But apparently those sorts of systems cost money, and I got loans, homie. If we look at each of these elements over the 160 individual seasons represented in the past five years, we should get at least a basic understanding of whether or not a team's secondary has a significant effect on its win total.

Below is a chart of the correlations for each of the four categories. As you probably guessed, "Adj. D. Pass NEP/P" stands for Adjusted Defensive Passing NEP per play.

Adj. Pass NEP/P0.68
Adj. Rush NEP/P0.36
Adj. D. Pass NEP/P-0.53
Adj. D. Rush NEP/P-0.28

So quarterbacks are kind of important. Glad we were able to establish that.

As a note of clarity, the negative correlations for defense are expected. This means that as a team's NEP decreases (which is better on the defensive side of things, as a defense "takes away" expected points), their win total increases. Both the Adjusted Passing NEP per play on offense and defense fall in the "moderate to strong" linear relationship range while the rushing categories are in the "weak to moderate" range.

As you can see, a team's passing defense was not as predictive of its win total as its passing offense. However, both dwarfed rushing offense and defense. Feel free to show this to Rex Ryan when LeSean McCoy has a $9 million cap hit in 2019.

Even if it's not as critical as a great offensive passing game, this should show that having a competent pass defense is important to team success. But that was not the original question. We wanted to see if the Jets could win if they had a studly pass defense while lacking on the offensive side of things. So let's look back through the past few years and find teams in similar situations to see how realistic the Jets' win-now aspirations are.

An Upward Battle

To evaluate this, I took a look at the teams that have had the best Adjusted Defensive Passing NEP per play marks of the past five seasons. This would be the best-case scenario for the Jets, although it should not be expected. Uncertainty abounds in free agency, so it's totally possible they don't even sniff these stellar metrics. But let's assume the best for argument's sake.

Since 2010, there have been 33 teams that have finished the season with a negative Adjusted Defensive Passing NEP per play (passing is a lot harder to stop than rushing, which is why there aren't more). Of those 33, 26 teams won at least 9 games. 10 of them won 12 or more games. If you can get this mark below zero, your playoff odds are quite tasty.

Sticking with those same 33 teams, 7 of them also had an Adjusted Passing NEP per play mark for their own offense that was below zero. These seven teams averaged 7.86 wins per season with three below .500, two finishing 8-8 and two above .500. This is a super small sample size, but it should at least be concerning for Gang Green faithful.

At the same time, the average Adjusted Passing NEP per play over this time period was 0.06. We're assuming the Jets will finish significantly below average in this statistic. Even the 2014 dumpster-fire Jets finished the year with an Adjusted Passing NEP per play of 0.02. Now, they've picked up a guy in FitzMagic who has a better track record than you might expect. Maybe Maccagnan and Todd Bowles are onto something here.

Let's assume that the Jets, with their new toys, take their Adjusted Defensive Passing NEP per play down to 0.00, which would be a very respectable mark, but certainly not other-worldly. If they then keep their other marks from last year the exact same (assuming no progression in the passing or rushing offense and a static rushing defense), then they would profile similarly to the 2010 Kansas City Chiefs.

Those Chiefs, led by a majestically mediocre Matt Cassel, finished the season 10-6 and made the playoffs. This, in no way, means that this is an expectation for the Jets. The only point of this is to show that it is possible to make the playoffs with quarterback play similar to that which the Jets received last year if you have an above-average secondary.

What the Jets have gotten in Darrelle Revis, Antonio Cromartie and Buster Skrine is three of the top six free agent corners on Evan Silva's Rotoworld rankings. Marcus Gilchrist graded as the sixth-best safety. They join recent first-round picks Dee Milliner and Calvin Pryor. That, on paper, looks like a group that could post the plus metrics necessary to compete on a team with a poor offense.

The conclusion here is that, yes, it's possible for the Jets to win with a top-notch secondary and poor quarterback play. It's just not the most likely scenario. If they want to get this team back into the playoffs, they will most likely need more than just that pass defense to get there. Decent quarterback play, though, would immediately shift the conversation and put this team back in business.

It's possible this entire experiment flops, and the Jets spend the next five years trying to dig their way out of a pit of lost money. But there's also the possibility that it works out. If Maccagnan and Bowles can take a ridiculed team from 4-12 to the postseason, they will have earned themselves a little vacation. I hear Anguilla is nice.