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Run Defense by Number of Backs 2018

5 min read
Run Defense by Number of Backs 2018


by Scott Spratt

The personnel and formation analysis we have previously done help to paint the picture of team strategies and effectiveness, but they do not complete it. Unlike in a sport like basketball, football teams have different objectives on different plays based on contextual factors like the down and distance. That context is critical for understanding their different choices of personnel and formations.

The Patriots illustrate that point perfectly. They led all teams in 2018 with 235 carries from two-back sets, the majority of which came with fullback James Develin as a lead blocker. Clearly, they were more willing than many teams to use a fullback at all, but they also consistently built leads and wanted to kill clock. They used Develin to do that, running with two backs on the field 61 percent of their attempts with a lead compared to just 47 percent when trailing.

The Patriots use their various running backs and fullbacks in a variety of creative ways, and so it may not be perfectly fair to paint their intentions with so broad a brush. But overall trends mirror that narrative. Even while teams’ reliance on multiple running backs has declined in recent seasons, they have maintained a consistent distribution of carries with two backs on the field based on their score differential.

That is a lengthy aside to open an article about run defenses against single- and two-back formations. But as I uncover and discuss team and league trends, keep context in the back of your mind. The percentage of two-back carries defenses face correlates with itself from year to year and correlates with rushing DVOA allowed against two-back sets within a year. That reflects consistencies in defenses’ strengths and weaknesses and opposing offenses’ attempts to take advantage of those strengths and weaknesses, but they also capture consistencies in things like schedules and overall team qualities that drive game scripts.

For the purposes of this analysis, we’re measuring rushing attempts by any player who was lined up in the offensive backfield but was not at the quarterback position. Single-back formations include any set where one player other than the quarterback was lined up in the backfield and ran the ball; two-back or multiple-back formations include any set where more than one player other than the quarterback was in the backfield, and one of those players ran the ball. The numbers include direct snaps to a player who was lined up as a running back but do not include scrambles, quarterback keepers, wide receiver or tight end end-arounds or reverses, or “Wildcat” style plays.

The seven defenses that faced the highest percentage of runs from two-back sets were all in the AFC. The Bills and Dolphins in first and third place each played the fullback-reliant Patriots twice in the AFC East, and they both also saw plenty of second-half power runs while being outscored by more than 100 points over the course of their seasons.

The Chiefs and their conference-leading +144-point seasonal scoring margin certainly cannot say the same. But their bottom-10 overall defensive DVOA skewed heavily toward the run. They were the worst run defense in football with a 9.8% DVOA (remember that positive DVOA numbers are bad for a defense) and were particularly bad against two-back sets at 15.1%. Their 4.7% pass defense DVOA was in the upper half of all teams, and much better than their run defense when you consider that passes average better DVOA numbers than runs in general. Teams were smart to run the ball to target the Chiefs’ biggest defensive weakness and limit the number of plays that Patrick Mahomes’ No.1 DVOA offense had the ball. Of course, the Patriots, Chargers, and Seahawks were the Chiefs’ only three opponents who could capitalize on such a game plan with a win.

The Patriots saw the fewest runs from two-back formations in great part because they didn’t face themselves. And perhaps because they have a chance to practice against James Develin every day, their defense performed much better against the handful of two-back sets they did face (-55.5% DVOA, best in football) than they did against single-back looks (-5.0%, 22nd).

The 49ers weren’t too far behind, facing two-back formations on just 16 percent of their opponents’ carries, and for much the same reason. But their defense enjoyed a +15.8% DVOA advantage against single-back sets over two-back sets and had a similar +9.6% advantage in 2017. Maybe that split is a result of a small sample size, but I think it might also reflect the team’s personnel. Strong safety Jaquiski Tartt is a major player in their run defense. He held opposing runners to 3.5 yards per carry, the best mark for qualified safeties in 2018. But Tartt is just 215 pounds. He can’t take on fullbacks the way a linebacker can. The team will hope that its new $54-million linebacker Kwon Alexander can anchor an improved power run defense.

Bryan Knowles pointed out the oddity that the Cardinals defense saw the lowest frequency of runs from two-back sets in 2017 despite playing in the same division as the fullback-happy 49ers. That normalized in 2018, and the Cardinals defense experienced the biggest gain in percentage of runs from two-back sets, 12 percent. That increase was one of the few things that went right for the team last year. They performed much better defending runs from two-back sets (-29.9%) than from single-back sets (4.2%).

There is likely a lot of noise driving the biggest defensive improvers versus two-back sets. None of the top-five gainers from 2017—the Patriots, Bears, Saints, Redskins, and Seahawks—faced even 100 such attempts last year. The DVOA improvers against single-back formations should be more telling with carry volumes between 200 and 300. Those leaders—the Texans, Jaguars, Bills, Bears, and Colts—matched up not only with the defensive rushing DVOA leaders but also with the overall defensive DVOA leaders.

Four of those five teams are transparently defensive-minded. Andrew Luck’s Colts are not. Rookie linebacker Darius Leonard was an obvious boon. He recorded 163 combined tackles, 19 more than any other player in 2018. But the Colts have remade their defense with a number quality young players. Sophomore linebacker Anthony Walker and sophomore cornerback Kenny Moore both held runners to 2.3 yards per carry, in the top three of qualified players at their positions. Malik Hooker couldn’t maintain his otherworldly rookie rate of interceptions and pass deflections in his second season, but he clearly disrupted offenses with his coverage, as evidenced by his miniscule 2.6 percent target rate (nine targets on 913 snaps). The team’s recent run of draft success saves them a lot of money, which should in turn help them plug their few remaining holes in free agency, such as with Justin Houston for their pass rush this offseason. Their balance should put the Colts on the short list of contenders over the next few seasons.



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