I have a question because I'm a little unclear on the concept of analyzing complex systems and so on. In school I took a business class called Quantitative Analysis, a method for determining mathematically what your business needs and how it's performing. It's a discipline that actually grew out of WWII, when they put mathematicians and business people to work figuring out things like, if you need X number of troops to lead an invasion, they'll need Y food rations and Z shovels and so forth. I did alright in the class but it's one of those things that hasn't had much practical use in my life so I forget how it all works.
But anyway, my question for the data miners and the analysis people is this: If you have the best of something and the second best of something, does that automatically mean you've got the best pair of that thing? Or can someone else that has neither No. 1 nor No. 2 somehow have a better duo than yours?
I ask because the droids over at NFL.com's advanced metrics factory just determined who they think the best coverage defensive backs in the league are:
The key metrics that will be considered in judging this group:
- Passer rating allowed
- Catch rate allowed below expectation
- Tight window percentage
- Target rate
- Average separation yards
Ballhawk rate and coverage-success rate will also be considered as supplemental metrics.
I know that's a lot to digest. Deep breaths, everyone. Let's dive into the top 10.
1. Stephon Gilmore
New England Patriots CB
Passer rating allowed: 38. Catch rate allowed below expectation: -11.8. Tight window pct: 27.1. Target rate: 19.5. Average separation yards: 2.7.
Gilmore cemented himself as the league's best corner in 2019 with numbers like the ones listed above, which don't even include his six interceptions. He was the only player who faced 85 or more targets and didn't give up a touchdown. He allowed the lowest passer rating as the nearest defender in coverage among cornerbacks in 2019 (teammate J.C. Jackson is listed as a defensive back). His catch rate allowed below expectation (-11.8) was also the lowest among cornerbacks with a minimum of 300 coverage snaps. No one was better in coverage than Gilmore in 2019.
2. J.C. Jackson
New England Patriots DB
Passer rating allowed: 21.8. Catch rate allowed below expectation: -10.1. Tight window pct: 27.6. Target rate: 15.6. Average separation yards: 2.2.
Jackson's numbers are slightly better than Gilmore's, but we need to consider a key stat here: targets. Gilmore posted a similarly excellent percentage in coverage, but did so on almost twice as many targets (96 versus Jackson's 58). Add in the fact that they play on the same team, with Gilmore serving as the No. 1 corner often tasked with the more difficult assignment, and Gilmore's performance looks slightly better. Having said that, Jackson was still a revelation for the Patriots despite starting just six games, allowing the lowest passer rating as the nearest defender in coverage among all defenders who qualified for this exercise, and the second-lowest completion percentage allowed. Jackson was excellent, especially in press coverage, allowing a passer rating of just 8.1 in such situations and recording all five of his interceptions while in press. No one was better in those two categories while in press. Add in his perfect passer rating allowed of 0.0 as the nearest defender on deep targets and you'll see the resume of a defensive back poised to explode onto the scene as a soon-to-be-household name in the same defense that also features Gilmore, the reigning NFL Defensive Player of the Year.
Huh. Interesting. That Stephon Gilmore the best pass defender in the league is something anyone from my mother-in-law to the crazy guy in town whose front lawn is covered with major appliances one of the residents of that isolated island where they'll kill people who come to preach the Bible could tell you without seeing the stats. That JC Jackson is the second best shouldn't come as a huge shock to anyone who paid attention last year. Like the unnamed executive who called him a Top 10 cornerback last month:
But back to my question, how is that everyone doesn't do the simple math and determine this automatically gives the Patriots the best pair of corners in the league? And don't try to get by on NFL.com's technicality that lists him as a defensive back and not a corner. You can't split that hair. Yes, not all DBs are CBs but all of the class of CBs are DBs and he is a corner in every sense of the word. Playing up on the line, outside or the slot. Solo covering receivers in man. Jamming them off the line. And generally doing corner things like corners do. You can't split that hair.
And yet, ask anyone in the business who the best cornerback tandem in the league is and you'll get an answer other than the best and the second best in the same uniform lined up on the same LOS every week.
- NFL.com themselves list Baltimore's Marlon Humphrey and Marcus Peters, with Gilmore and Jason McCourty No. 2.
- Bleacher Report does likewise.
- CBS Sports takes the whole position group, including McCourty and Jonathan Jones, calls them "the best cornerback group in the NFL for most of last season" and still puts them behind not only Baltimore's, but also Desmond King and Casey Heyward of the Chargers.
I could go on but I think I've made my point.
So the national punditry is behind the analytics when it comes to this particular position on this particular team. Fine. That's almost always the way science works. There are still people walking among us who still eat according to the old model of the Food Pyramid. Although they're not so much walking as they're riding through the supermarket on Handifat scooters because their carb-inflated elephantine legs can't carry them to the bread aisle and back. It takes a while for perception to catch up with data.
My question is more for the Boston media people who positively hammered Belichick for signing Gilmore when Malcolm Butler was looking for his payday. And then again when he let Butler walk instead of matching Tennessee's offer of five years and $61 million. (I'm not talk about sitting him in the Super Bowl. That's a discussion for another time). As much as I love Butler, his story, and all he'll represent from now until the Heat Death of the universe, JC Jackson has been better Butler is, ever was, and probably ever will be again. And he's still two seasons away from having the leverage to leave as Butler did. Letting an eternal folk hero go was tough. But it's a move that has worked out spectacularly well.