Defensive Personnel Analysis 2019

Earlier this week, we looked at which personnel groupings were most popular on offense in 2019. Now, it's time to flip that around and look at how defenses have responded.

It's not new that the term "base" defense no longer accurately describes modern defensive design; the days of teams trotting out seven men in the box down after down after down are, at the moment at least, as anachronistic as a team coming out in the old seven-diamond would be. Base defense did make a slight resurgence this past season, but it's still used on under 30% of all defensive snaps; it has become a situational front used against certain matchups, rather than the foundation of defensive strategy.

This, of course, is a reaction to 11 personnel taking over the league; it's simply hard to match up against three wide receivers with just four defensive backs. The slight resurgence of two-back or two-tight end sets made base slightly more palatable last season, but even then, that second tight end or running back is more likely to be a passing threat now than they were in the 1980s, so it's frequently easier just to leave that nickel corner out there and call it a day. In fact, teams saw more use of dime defense in 2019, as getting more and more defensive backs onto the field remains the agreed-upon strategy to handle modern NFL offenses.

A couple quick notes before we continue:

• For the record, 54% of base snaps were in 3-4 and 44% were in 4-3; that's almost an exact mirror of their totals from 2018. That doesn't add up to 100%; there were 133 snaps of 2-5 (most frequently from the Jets), 65 snaps of 5-2 (often from San Francisco or Tampa Bay), six snaps of 1-6, and even two of 0-7 (Chicago had a real "how do I hold all these linebackers?" problem at times). However, as we note in the book, it can be tough to differentiate a defensive end from a linebacker in modern defenses.
• While we group 4-3 and 3-4 defenses together at this point, the majority of teams do still use one or the other more or less exclusively. 13 teams were primarily 3-4 units, including, surprisingly, New England -- they had used a fairly even mix of 3-4 and 4-3 in 2018, but ran just three snaps of 4-3 last season against 133 snaps of 3-4. That might be the Jamie Collins effect there, so we'll see what happens in 2020 now that Collins is in Detroit. Nine teams were primarily 4-3 units, led by Indianapolis, although the Colts did see an increase in their 3-4 snaps -- specifically, going from zero to three. That leaves ten teams which saw neither front hit 75% of their base snaps -- the Falcons, Panthers, Bears, Jaguars, Dolphins, Jets, Buccaneers, Lions, Chiefs, and Saints. That's an increase from 2019; we'll stick a pin in that and see if that's a trend rather than random noise.
• "Dime+" includes any package with more than five defensive backs. That includes all your dime packages, as well as the 299 snaps in quarter, 22 snaps with eight defensive backs on the field (… half-dollar?), and even four snaps with nine defensive backs (… the Sacagawea package?). If you're curious as to what a play with nine defensive backs looks like in practice, it's the pinnacle of optimum play:
  

  Line was Niners -10. They were losing with 40 seconds to go and then this. Worst bad beat I've ever seen pic.twitter.com/UG6vc8yB6P
  

  -- Ben Koo (@bkoo) November 18, 2019

• "Big" defenses are 4-4 or 3-5 lineups, while "goal line" includes all other personnel groups with fewer than four defensive backs. More than half of those defenses were used on the 1-yard line, but that wasn't a literal necessity; the Lions even busted out a "goal line" look on their opponent's 13-yard line as they sold out to stop the run.

Last season, defenses did have a better DVOA in base than they did in any of these new-fangled multi-defensive back formations, and that's fairly typical. That does not, however, mean that base defense is better and every defensive coordinator in the league is getting things wrong. It's a matter of matchups more than anything else. Base defense continues to vanish against 11 personnel, the most effective offensive personnel group. There were about 1,500 snaps of base defenses against 11 personnel in 2017, 1,000 in 2018, and just 660 in 2019, mostly due to one team (we'll get to that). The median team played just six snaps of base defense against three-wide sets.

Teams do actually have a better DVOA against 11 personnel in base than in nickel or dime, but that's almost entirely due to the offense's run/pass ratios; defenses use base personnel when they think the opposing offense is going to run. So while nickel and dime+ defenses ended up facing pass attempts on 72% of their snaps against 11 personnel, base defenses faced passes only 59% of the time -- and those passes were, on average, a full yard shorter than the ones faced by nickel packages. That right there explains most of base's relative success against 11 personnel; they faced easier situations. Much of the rest of it can be explained by selection bias; if your team can't match up base against 11, you're simply going to run nickel defense -- or you're going to get fired.

Now that we've talked about the league-wide trends, we can talk about team-specific oddities. That requires the annual big honkin' table, which we have here.

Alright, I said we'd come back to the one team who stubbornly played base against 11 personnel, so hi, Seattle! The Seahawks had 217 snaps in base against 11 personnel; no other team had more than 60. Seattle played 69% of their snaps in base formation, which is mind-boggling. Two years ago, we mocked Cleveland relentlessly for going in base 66% of the time in their 0-16 season; they were the only team since 2014 to use base over 60% of the time. Now they have company; a defense rushing out a front seven at a rate we have not seen since the three-receiver revolution took over the NFL. When we talked about the Browns, we laughed and moved on; they were terrible, so of course their terrible defensive strategy was also terrible. But the Seahawks were a playoff team last season; they were an inch away from winning the NFC West. As such, this one deserves a bit of a closer look.

First and foremost, Seattle was correct in shying away from their nickel package. They had a -3.4% DVOA in base personnel, compared to a 30.4% DVOA in nickel. That puts them squarely in the middle of the pack in base DVOA but dead last with five defensive backs on the field. It is rare for a defense to be that much worse in one particular personnel group than another. Take Miami, for instance -- they had the second-worst DVOA in nickel at 27.4%, but their overall DVOA was 21.8%; no real change there. The Seahawks had a 2.6% overall defensive DVOA, and yet were Dolphins-esque with that fifth defensive back out there. Opposing offenses had a 41.4% DVOA against Seattle when they were in nickel -- that's adjusted for how good the Seattle defense was overall, and the Seahawks were giving up a full yard per play more than they were in base. No other defense allowed their opponents to have an offensive DVOA of over 15.7% when they were in nickel defense. For the Seahawks, switching from base to nickel was the equivalent of swapping the opposing offense from last year's Colts for the 2010 Patriots. More like the Legion of Bust, am I right?

For comparison, the 2017 Browns went from a -0.2% DVOA in base to a 12.3% DVOA in nickel -- they, too, were better in base, but not to the extent that Seattle was. And the Browns were significantly worse against the pass in base defenses than they were in nickel, meaning that they weren't doing a good job of matching personnel to situation. Against the pass, the Seahawks had a 0.3% DVOA in base and a 31.2% DVOA in nickel. Their extremely high level of base defense isn't because of poor game planning or adherence to a terrible philosophy; it's because their nickel package was terrible. They only went to it when they were absolutely sure that they were facing a pass. Their nickel sets faced only 19 runs all season long. It should be noted that the nickel package only marginally improved to 24.9% when Quandre Diggs arrived midseason. The issue was that their planned third corner, Jamar Taylor, was a disaster; the Seahawks were just better off keeping K.J. Wright and Mychael Kendricks on the field. Pete Carroll has always liked base more than most of his contemporaries, but never to this extent, and never with this big of a split in outcomes. This was a change caused by a specific personnel situation, and should be temporary. After all, the Seahawks brought in Quinton Dunbar to lock up that slot corner spot and … oh. Well, maybe someone will rise to the occasion this season.

Seattle's not the only team which had to do some strategic reshuffling due to personnel issues. The Chargers went from playing dime+ 64% of the time in 2018 to just 19% last season, due in part to Derwin James' injury and also to actually having healthy linebackers for once. Other teams saw their defensive philosophies shift wildly thanks to the rotating chairs of defensive coordinators last season. The 2018 Cardinals led the league in nickel usage at 84%; Steve Wilks brought that with him to Cleveland which went from 66% to 85%, most in the league. Wilks was replaced in Arizona by Vance Joseph; his 2018 Broncos had led the league in base usage at 45% and so Arizona saw its base defense jump from a dead-last 10% in 2018 to 38% in 2019, first in the non-Seahawks division. And with Joseph gone, the Broncos brought in Vic Fangio -- Fangio's Bears had a 76% nickel usage in 2018, and Denver's nickel usage jumped from 27% to 65% last season. It makes you long for the stability in Buffalo, which went from 21%/77%/1% in 2018 to 22%/77%/0% in 2019; they were the only team in 2019 to run zero plays with more than five defensive backs on the field.

Most teams' frequencies went nickel-base-dime; that was the order for 22 teams last season. You can split them into subgroups, of course. Teams such as the Bills, Browns, and Jets basically lived in nickel and only brought in an extra front seven player in absolutely sure running situations, while teams such as the Dolphins, Colts, and Bengals flipped from nickel to base to dime all willy-nilly. Of these 22 teams, the Browns are probably the most interesting; even in the modern NFL, sticking in nickel 85% of the time really jumps out at you. Was it effective? Yes. Ish. The Browns ranked 17th in nickel DVOA at 1.6%; in all other personnel groupings, they were dead-last at 29.0%. I'm not sure the "we're No. 17!" foam fingers are going to sell particularly well, mind you, and the Browns had been fifth in non-nickel DVOA in 2018; you could make the argument that Wilks fixed the nickel defense at the expense of everything else.

The second-most common pattern was nickel-dime-base, with teams pretty much eschewing an extra linebacker for a third safety most of the time. Some of this can be directly traced back to Bill Belichick: you have his Patriots, defenses led by his former assistants Matt Patricia (Lions) and Jim Schwartz (Eagles), and a defense led by his former player Mike Vrabel (Titans). Ex-Patriots coach Brian Flores' Dolphins nearly joined the group as well and probably will in 2020. The Ravens, Chiefs, and Saints round out this crowd, giving us six defenses that finished in the upper half of the league and then also the Lions. Some of the heavy defensive back usage may be based on the fact that a lot of these teams were winning a lot, so their opponents were passing a lot, so more defensive backs were needed, but this wasn't just about teams bleeding out leads with extra backs. The Patriots and Ravens, especially, made three-safety packages a huge part of their look and it paid massive dividends. It makes sense -- you don't want a third or fourth linebacker on the field because it's no longer the 1980s, but you don't want to lose that physicality in the box entirely, so you stick an extra safety out there to improve your pass defense without harming your run defense entirely. Maybe in ten years' time, we'll be listing third corners and third safeties as starters and pining for the good ol' days where you might see a front six.

The Packers took this philosophy to the extreme last season, as they were the only team to go dime-nickel-base. They only ran 201 plays without an extra defensive back, and their 510 snaps of dime+ were 77 more than the second-place finisher. Without a true three-down linebacker to play next to Blake Martinez, the Packers saw their dime+ percentage rise from 41% in 2018 to 51% last year; coupled with the Chargers' drop-off, that gives them the dime-usage crown. I'm not sure they would have passed the 50% mark if they had had more options at linebacker, but Mike Pettine does like the versatility in coverage you get from three safeties. You do wonder if that over-reliance on dime schemes ended up hurting the Packers in the playoffs when San Francisco ran over them, though I'd caution against using one bad game as a massively significant datapoint. After all, the Packers were better against the run then the Seahawks, who we already established lived in base personnel.

That covers 31 teams, leaving just the Rams, the only dime-base-nickel team in the league last season. In 2018, the Chargers were the only DBN team in the league, so the title has just moved across town. But the Chargers became more and more of a dime-first defense as the year went on in 2018, as Derwin James blossomed and the linebackers joined the IR. The Rams went on the opposite journey, running 50 snaps of nickel in the first half of the year and 193 the rest of the way -- or, to put it another way, going from 32nd to 24th in nickel frequency. That means they did a complete flipflop, ending the year as a nickel-base-dime team, albeit with a fairly even split between the three -- 33%/37%/29%. I expect that's at least in part due to John Johnson's injury, though it will be interesting to see how the Rams shape up with a healthy lineup in 2020.