by Bryan Knowles

Earlier this week, we looked at 2017 run offense by number of backs. Today, we'll flip sides and look as how defenses handled the running game with and without extra men in the backfield.

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 mean one player other than the quarterback was lined up in the backfield and ran the ball; two-back or multiple-back formations mean 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 "Wildcat" style plays.

First, it should be made clear once again that there is not much of a correlation between a defense's skill at stopping one- or two-back sets and the frequency with which they face them. The correlation between the frequency a team faced two-back running and their DVOA difference when facing two-back running was 0.28. There's a very, very broad general trend towards teams who were poor at stopping two-backs seeing extra fullbacks and H-backs throughout the year, but it's inconsistent from team to team and seems more like noise as opposed to strategic decisions by opposing offenses.

Last year, we noted that the teams that had to face two-back sets the most in 2016 performed poorly as a whole against them; that eight of the 11 teams that faced at least 100 two-back sets fared worse against them than against one-back sets. It turns out in retrospect, that was a blip. It's nearly 50/50 this year, and the correlation was roughly the same as in 2017. Instead, the biggest factor in how much two-back running you'll be facing is just your schedule.

The Browns, for instance, played in the division with the most two-back sets (the AFC North) and played against the division with the second-most two-back sets (the AFC South). It should come as no surprise, then, that Cleveland's defense faced more two-back running plays than any other team in football. They were actually better at defending two-back sets than single-back sets, so it's not a strategic decision by Cleveland's opponents to attack them with extra men in the backfield. Cleveland's opponents used two-back sets against everyone else, so of course they used them against Cleveland, too. There's a 0.71 correlation between the frequency your opponents used two-back sets in general and the frequency they used them against you. Teams aren't generally taking H-backs out of mothballs to challenge your team; they're running their normal offense without regard to your team's strengths and weaknesses.

The best way to use the following table, then, is not to go "oh no! My team is particularly bad at stopping two-back running, so everyone's going to load up the backfield and pound it down our throats all season long!" or vice versa. Instead, if your team is particularly bad or good at one split or another, you can glance at the schedule to see how many fullback-loving teams they'll be scheduled to face, and that will tell you how much of a problem or benefit it's likely to be going forward.

2017 Defense: Running with 1 or 2 RB in Formation (Not Personnel) Defense Pct 2+ RB Rk 1-RB Rushes 2-RB Rushes Difference Runs Y/A DVOA Rk Runs Y/A DVOA Rk Y/A DVOA Rk CLE 38% 1 246 3.6 -30.4% 2 153 3.0 -33.2% 4 0.5 2.9% 15 HOU 37% 2 237 4.3 -12.7% 16 137 3.3 -18.0% 15 1.0 5.3% 14 MIA 33% 3 244 4.5 -10.9% 19 122 3.1 -19.5% 12 1.4 8.6% 10 PIT 33% 4 230 4.2 -15.3% 14 111 4.9 3.9% 29 -0.7 -19.3% 30 CAR 32% 5 200 3.5 -27.6% 3 95 4.7 -9.9% 19 -1.2 -17.6% 29 OAK 31% 6 261 4.1 -13.1% 15 120 4.1 -12.1% 18 0.0 -1.1% 20 CIN 31% 7 299 4.2 -9.3% 21 133 3.6 -8.2% 22 0.5 -1.1% 21 BUF 31% 8 278 4.2 -2.2% 30 123 5.2 7.8% 31 -1.0 -10.0% 26 IND 30% 9 297 4.4 -10.3% 20 129 3.0 -30.1% 5 1.5 19.8% 3 NO 29% 10 240 4.1 -18.6% 10 99 4.0 -7.9% 23 0.1 -10.7% 27 ATL 29% 11 230 4.0 -16.1% 12 92 3.6 -17.2% 16 0.4 1.0% 16 TB 28% 12 260 4.6 -5.0% 29 102 3.3 -22.7% 10 1.3 17.7% 6 BAL 27% 13 282 3.9 -11.3% 18 106 4.1 -25.2% 9 -0.1 13.9% 8 SEA 26% 14 283 3.5 -22.6% 6 101 5.0 8.0% 32 -1.5 -30.6% 32 LAR 26% 15 273 4.6 -9.1% 22 96 4.8 -2.1% 28 -0.2 -7.0% 24 NYJ 26% 16 299 3.8 -18.8% 9 105 3.8 -12.8% 17 -0.1 -5.9% 23 Defense Pct 2+ RB Rk 1-RB Rushes 2-RB Rushes Difference Runs Y/A DVOA Rk Runs Y/A DVOA Rk Y/A DVOA Rk DET 26% 17 276 4.4 -5.8% 28 96 3.6 -5.0% 26 0.8 -0.8% 19 KC 25% 18 286 4.5 0.2% 32 97 3.3 -19.2% 13 1.3 19.4% 4 GB 25% 19 304 3.7 -23.5% 5 102 4.1 -2.7% 27 -0.5 -20.9% 31 JAX 25% 20 268 4.3 -5.9% 27 87 4.3 -20.2% 11 0.0 14.3% 7 MIN 24% 21 232 3.6 -20.8% 7 73 3.4 -27.0% 6 0.1 6.2% 13 CHI 24% 22 289 4.3 -12.4% 17 89 3.7 -7.3% 25 0.6 -5.1% 22 DEN 20% 23 300 3.8 -15.4% 13 75 2.1 -53.2% 2 1.6 37.8% 1 WAS 19% 24 326 4.5 -7.6% 24 75 4.3 7.3% 30 0.2 -14.9% 28 NE 18% 25 268 4.8 -0.8% 31 60 3.8 -9.4% 20 1.0 8.5% 11 TEN 17% 26 285 3.4 -19.0% 8 60 3.4 -26.3% 8 0.0 7.3% 12 SF 16% 27 339 3.8 -16.9% 11 66 4.2 -7.3% 24 -0.4 -9.6% 25 PHI 16% 28 239 3.5 -34.6% 1 44 2.7 -34.2% 3 0.7 -0.4% 18 NYG 15% 29 340 4.2 -8.2% 23 60 4.0 -18.4% 14 0.3 10.2% 9 LAC 15% 30 319 4.4 -7.4% 26 56 6.0 -8.3% 21 -1.6 0.9% 17 DAL 15% 31 285 4.4 -7.5% 25 50 2.8 -26.5% 7 1.6 19.0% 5 ARI 12% 32 304 3.5 -27.2% 4 40 2.4 -60.0% 1 1.2 32.9% 2 NFL 25% -- 8,819 4.1 -13.6% -- 2,954 3.8 -14.8% -- 0.3 2.2% --

Volume Comparisons

We would like to remind fans of Arizona and Philadelphia that it is, in fact, legal to have multiple players in the backfield at the time of the snap.

The Cardinals and Eagles faced the fewest and second-fewest two-back runs in 2017. They also had the fewest and second-fewest two-back runs in 2017. This isn't, as far as we can tell, a charting glitch or some kind of weird data entry error; this is a real thing that occurred.

Arizona stands out in particular. They only faced 40 two-back rushes all year long despite playing San Francisco twice, the team with most two-back runs in football. The 49ers were responsible for 15 of those 40 rushes all by themselves. If you were a Cardinals fan with other plans on October 1 and November 5, you saw just 30 two-back rushes in Cardinals games all season long.

We're not quite at the point where we have single games in our database that saw more two-back rushes than a team did all season long, but we're approaching that point rapidly. We started keeping track of two-back rushes in 2008. The ten teams that saw the fewest number of combined offensive and defensive two-back rushes all played in the last three years.

Fewest Combined 2 RB Rushes in a Season Year Team Off Runs Def Runs Total 2017 ARI 5 40 45 2017 PHI 8 44 52 2016 ARI 14 75 89 2016 PHI 15 82 97 2016 WAS 31 66 97 2015 PHI 9 89 98 2015 NE 40 64 104 2017 WAS 40 75 115 2016 NYG 30 85 115 2017 NYG 56 60 116

Arizona's 40 two-back rushes faced is the new low in our database, and Philadelphia's 44 tied the record set last year by Atlanta; it's no longer just a few teams tamping numbers down, but a league-wide phenomenon. When everyone in the league is using fewer two-back sets, it ups your chances for setting new records.

While schedule remains the largest factor in determining two-back frequency, it's not the only one. Putting yourself in positive game script situations is a way to keep your numbers down. When you have large leads, your opponents aren't going to be able to rack up power, run-out-the-clock sets. Even fullback and H-back-happy teams are going to have to spread more receivers out if they find themselves facing large deficits. That's one of the reasons Philadelphia faced so few two-back runs last season—they were, on average, up 5.1 points at any given point in a game, the third-highest total in the league. Teams passed against Philadelphia a league-leading 65.4 percent of the time; you can't face two-back runs if the other team isn't running at all.

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It's quite possible that no one will catch Arizona and Philadelphia next year, even with the league-wide trend of two-back running going down. Arizona now has to face not only Kyle Shanahan but also Brian Schottenheimer twice a season. Philadelphia has a better chance, with their high game script and the lack of two-back rushing in the NFC East, but they have to take on the AFC South next year, and the Jaguars and Titans loved their two-back sets a year ago. Matt LaFleur's arrival might in Tennessee might see that change going forward, but the smart money would be on no one seeing as few as 40 two-back rushes a year from now.

The AFC North and AFC South had the most two-back rushing a year ago, so it's no surprise to see Cleveland, Houston, Cincinnati, and Indianapolis leading the league in two-back plays defensively. The AFC North was the only division where all four teams faced at least 100 two-back snaps; they still play old school football in the Midwest. All four teams faced more two-back sets in 2017 than they did in 2016, with Cincinnati and Pittsburgh being two of the three teams with at least 50 more. Credit that jump, at least in part, to going from playing the NFC East, where two-back running goes to die, to facing the AFC South. Greg Roman's arrival in Baltimore also pushed up the numbers for the other three teams in the division.

The team that saw the greatest increase was Buffalo, who went from 15 percent to 31 percent last year, adding 65 more snaps against two-back sets. That's a little harder to explain, as none of the other AFC East teams saw their numbers increase dramatically. Buffalo has been significantly worse at stopping two-back runs three years in a row, so perhaps teams are beginning to make different strategic decisions against them. Then again, Buffalo changed alignments and coordinators last season, so it's not like you'd expect all the defensive trends to carry over. Very peculiar. And no, there was no difference in frequency of two-back runs faced between 3-4 and 4-3 defenses. If anyone has an explanation for Buffalo, I'd like to hear it.

The 49ers saw their two-back plays drop off the most, as they went from two games against Jeff Fisher to two games against Sean McVay. That drop-off didn't affect Seattle or Arizona that much, because it was effectively canceled out by the swap from Chip Kelly to Kyle Shanahan. No one division saw all four teams face fewer two-back plays, but the AFC West came close; Kansas City stayed about even while everyone else dropped between 20 and 60 plays.

Efficiency Comparisons

We mentioned above that 3-4 and 4-3 defenses faced the same amount of two-back runs. They did not have the same effectiveness. 3-4 defenses, on average, saw their run DVOA improve by 4.4% when going from one-back to two-back sets. 4-3 defenses only saw a 0.5% improvement; basically statistical noise.

Is that an actual trend, or is it a statistical glitch? I lean towards the latter. The four teams with the greatest DVOA improvement in two-back sets all ran three-man fronts in 2017, but so did three of the bottom five. Denver and Arizona, each of whom saw their DVOA improve by more than 30 points in relatively small sample sizes, are skewing the numbers. If you only look at teams with at least 100 plays against two-back sets, 3-4 defenses drop by 1.2% while 4-3 defenses drop by 2.1%—and that's mainly Seattle dragging them down there.

And oh boy, did Seattle drag them down. We mentioned last week that the NFC West was weird, and that holds true on the defensive side of the ball as well. Seattle had the single hardest time dealing with two-back sets in 2017, falling a whopping 30.6% when having to deal with fullbacks and H-backs. That's nearly 10 percentage points more than any other team, and it's with a decent sample size of 101 snaps, as well.

Seattle ranked 14th in overall run defense DVOA in 2017, but it was a case of two wild splits averaging out to something normal. They were the sixth-best team in football at stopping single-back attacks, but dead last when faced with the likes of Kyle Juszczyk. Maybe this explains why they brought in three fullbacks this offseason -- they have an overinflated sense of just how dangerous a loaded backfield can be.

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Seattle played two games against the 49ers, the team with the most two-back runs in 2017. They also played two games against the Cardinals, the team with the fewest two-back runs in 2017. Seattle had a -6.3% rushing DVOA against the 49ers, allowing 5.7 yards per play. They had a -20.0% rushing DVOA against Arizona, allowing 2.8 yards per play. They throttled the single-back attacks of Washington, New York, and Philadelphia. They floundered against the two-back attacks of Green Bay, Tennessee, and Jacksonville. The Packers and Steelers also had significantly more trouble dealing with two-back rushing, but none of them saw quite so stark a division as the Seahawks.

Arizona will be glad to see Brian Schottenheimer arrive, as one of two teams to see their DVOA improve by 30 percentage points when facing two-back sets, but both they and Denver had a relatively small sample size to deal with. The team that really struggled the most against single-back running was Indianapolis. Not much went right in Indy last season, but they did have the 10th ranked run defense in the league. That dropped to 20th when facing single-back sets. The split isn't as stark as the one in Seattle, as Indy had bad days against two-back teams and good days against one-back teams. In general, though, the Colts were much worse when they were forced into nickel and dime packages, and teams capitalized in both the running and passing games.