by Sterling Xie

As football fans gobble through the flavorless buffet of player rankings, we're livening up the offseason's dog days by unveiling some of the charting stats that will appear in Football Outsiders Almanac 2015 (coming soon!). After looking at offensive rushing success by number of backs last week, we're flipping over to the other side of the ball and breaking down defensive success versus single- and multi-back formations.

As previous versions of this article have discussed, the number of two-back runs a defense sees doesn't really correlate with a team's record or DVOA. In other words, bad teams aren't necessarily seeing a ton of two-back sets from opponents trying to run out the clock. So although the Bucs and Bears faced a ton of two-back sets while the Patriots and Packers saw the fewest, that doesn't explain the Raiders seeing the third-fewest two-back sets or the Eagles seeing the third-most.

The connection between defense's success against two-back sets and the frequency of those sets is also fairly weak. Last season, the correlation between percentage of two-back runs faced and two-back run DVOA was 0.20, which isn't bad when you consider the sample we're dealing with (remember that positive defensive DVOA is bad, so we'd expect bad two-back defenses to see a higher percentage of two-back runs). Seven teams faced fewer than 100 two-back runs all season, while Tampa Bay was the only squad to face more than 170. So the fact that there's a positive correlation at all seems to indicate that most offenses are willing to alter their personnel a bit against poor power run defenses. However, when going back to 2008, it appears that this relationship is growing weaker:

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Taking the square root of the r-squared value, we get a correlation of 0.33 over the past seven seasons, indicating that offenses are becoming less interested in whether or not they can bulldoze their way over defenses. That's hardly a new discovery, of course, and we're already seeing the implications of this on roster construction. Talented run-stuffers like Terrance Knighton and Nick Fairley twisted in the wind on the free-agent market this spring before ultimately signing one-year deals. The Age-Adjusted Value metric Andrew Healy developed this spring suggests that these kinds of players are becoming good values, but that's also a byproduct of the lowered benchmarks they need to hit. Controlling the line of scrimmage remains as important as ever, but that mantra doesn't mean the same thing that it did 10 or 20 years ago.

We'll zoom the focus in on specific teams in a minute, but first let's get to the numbers. The table below includes yardage and DVOA stats for single- and multi-back formations. No Wildcat-style runs were counted, so plays involving direct snaps to running backs or receivers were left out of the study. The table is sorted by two-back rushing play percentage, and in the difference column, a negative DVOA means a team was worse defending runs out of two-back formations than it was against one-back formations.

Run Defense by Number of Running Backs, 2014 Def Pct 2+ RB Rank 1 RB 2+ RB Difference Avg DVOA Rank Avg DVOA Rank Avg DVOA Rank TB 53% 1 4.0 -32.1% 2 3.9 -10.9% 24 0.1 -21.1% 32 CHI 42% 2 4.2 -11.1% 15 4.5 2.7% 28 -0.2 -13.8% 30 PHI 41% 3 3.7 -24.4% 4 3.5 -21.2% 13 0.2 -3.2% 23 NO 41% 4 4.5 -1.0% 29 5.1 5.7% 31 -0.6 -6.6% 26 WAS 40% 5 4.0 -14.2% 10 3.8 -29.6% 6 0.2 15.4% 7 MIN 38% 6 4.9 3.2% 31 3.9 -5.6% 26 1.0 8.7% 15 SEA 38% 7 3.6 -30.7% 3 3.4 -23.3% 11 0.2 -7.4% 29 SF 37% 8 4.1 -12.8% 12 3.9 -20.1% 14 0.3 7.2% 16 SD 36% 9 4.2 -19.3% 8 4.1 -12.2% 23 0.1 -7.1% 28 DEN 36% 10 4.3 -20.2% 7 2.3 -42.7% 2 2.0 22.6% 3 MIA 36% 11 4.5 -8.4% 18 3.4 -20.0% 15 1.1 11.6% 11 ATL 35% 12 4.1 1.5% 30 4.0 -4.7% 27 0.1 6.2% 17 CLE 34% 13 4.3 -2.0% 26 4.7 4.6% 30 -0.4 -6.7% 27 STL 33% 14 4.2 -22.2% 5 3.8 -23.8% 8 0.4 1.6% 20 BAL 33% 15 3.6 -21.4% 6 3.1 -32.7% 4 0.5 11.3% 12 TEN 33% 16 4.7 4.1% 32 3.5 -10.6% 25 1.3 14.7% 8 Def Pct 2+ RB Rank 1 RB 2+ RB Difference Avg DVOA Rank Avg DVOA Rank Avg DVOA Rank CAR 32% 17 4.3 -12.7% 13 4.8 -12.9% 20 -0.5 0.2% 22 DAL 32% 18 4.8 -3.1% 25 3.6 -15.9% 17 1.2 12.9% 9 NYG 32% 19 5.0 -3.7% 24 4.3 -13.2% 19 0.7 9.4% 13 JAC 30% 20 4.4 -6.2% 21 3.2 -19.0% 16 1.2 12.8% 10 IND 30% 21 4.4 -3.7% 23 3.8 -23.5% 10 0.6 19.8% 6 DET 30% 22 3.2 -37.8% 1 3.0 -31.4% 5 0.3 -6.3% 25 HOU 30% 23 4.4 -1.7% 27 3.5 -23.6% 9 0.9 21.9% 5 CIN 29% 24 4.5 -1.6% 28 3.9 2.8% 29 0.6 -4.4% 24 PIT 28% 25 4.6 -4.6% 22 3.6 -27.0% 7 1.0 22.5% 4 KC 28% 26 4.8 -6.3% 20 5.3 13.1% 32 -0.5 -19.4% 31 NYJ 27% 27 4.2 -10.4% 17 2.6 -39.8% 3 1.6 29.4% 2 BUF 26% 28 4.0 -14.1% 11 4.2 -23.3% 12 -0.3 9.2% 14 ARI 25% 29 4.5 -17.6% 9 2.7 -47.6% 1 1.8 30.0% 1 OAK 25% 30 4.2 -10.6% 16 3.6 -14.7% 18 0.6 4.0% 19 NE 23% 31 4.2 -11.9% 14 3.5 -12.4% 21 0.7 0.5% 21 GB 19% 32 4.2 -7.6% 19 3.8 -12.2% 22 0.4 4.7% 18 NFL 33%

4.3 -10.7%

3.8 -15.7%

0.5 5.6%



The league-average DVOA against two-back runs improved -4.3% from 2013, the biggest year-over-year change we've seen since the average dropped from -4.9% in 2009 to -9.8% in 2010. One-back defense didn't improve nearly as much, but still dropped -2.5% from 2013. This won't come as a surprise if you recall from the offensive version of this article that run efficiency in general is languishing, as both the best and worst run defenses are seeing improvements.

(A reminder that overall league-wide run DVOA actually averages below zero because team DVOA stats such as these have a baseline built off of all plays: passing and rushing, plus certain penalties. Since passing is more efficient than rushing, the league average for team passing is always positive and the league average for team rushing is always negative. This is not true of individual DVOA ratings since those ratings only compare passing to passing and rushing to rushing.)

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Arizona and Denver actually posted the best two-back run defense DVOAs we have ever measured; previously, only the 2011 Lions had cracked the -40.0% DVOA barrier against two-back sets. In Arizona's case, defending two-back sets so well likely pushed their divisional opponents out of their comfort zones. The Cardinals faced the fourth-lowest percentage of two-back runs (25 percent) despite playing in the NFC West, which housed the two most frequent two-back users (St. Louis and San Francisco) as well as Seattle, which saw a big decline in two-back usage but nevertheless fared very well when they did choose to use a fullback (8.4% DVOA, second-best in the league). Both defenses ended up losing their defensive coordinators (Todd Bowles, Jack Del Rio) and starting nose tackles (Dan Williams, Terrance Knighton) this offseason, so they could be hard-pressed to replicate those lofty standards in 2015.

If the rich are getting richer, then the poor aren't nearly as destitute as they once were. The Chiefs brought up the rear with a 13.1% DVOA against two-back runs last season, but that was the best "last-place" DVOA we've measured since 2010. Kansas City's average run defense from 2013 suffered after the removals of Derrick Johnson and Eric Berry from the middle of its defense, as no player on the Chiefs front finished higher than 38th at his position in run stop percentage, according to our charting stats. Dontari Poe has done his best Atlas impression in shouldering the run defense alone, but after an elite run-stuffing rookie season, the mammoth nose tackle has seen his efficiency crumble under an untenable workload. (More help from the ends on either side of him certainly wouldn't hurt.)

Kansas City may have been the worst two-back run defense last year, but the Chiefs won't mind if they experience the type of revival their predecessor did. The Cowboys finished dead last in two-back DVOA in 2013 (16.1%), but experienced the biggest year-to-year improvement, dropping down to -15.9%, a -32.0% improvement that placed Dallas 17th overall in the category. Most of our numbers saw the Cowboys' defense as a middling smoke-'n'-mirrors unit, and while this area was no different, it counts as a win for a front that looked hopeless following Sean Lee's ACL tear. Tyrone Crawford has won the unofficial "Unoriginal Sleeper Who Everyone Labels a Sleeper" award this offseason, but most of that has centered around his pass-rushing potential. In reality, Crawford already has an elite run-stuffing season under his belt. Crawford's run tackles allowed an average gain of just 1.0 yard (fourth-best among edge rushers) with a 92 percent stop rate (third-best). Greg Hardy and Randy Gregory are receiving tons of attention (for better or worse), but Crawford seems like one of the few players on Dallas' defense that doesn't elicit a divisive response.

We haven't talked too much about one-back defense yet, mostly because the teams that were good against old-school I-formations could still stop the run when offenses ditched the fullback. The Lions led the way in single-back DVOA, but they also finished fifth against two-back sets. Detroit wasn't alone, as six teams finished in the top 10 against both types of runs. Only two teams finished in the top 10 against two-back runs but in the bottom 10 against one-back runs: Houston and Indianapolis. The Colts in particular got much worse against single-back rushes, as their 14.8% DVOA change was the third-worst regression from 2013. For all of Indy's signings this offseason, they kept the weakest part of their roster mostly intact, apart from a Cory Redding-for-Kendall Langford swap. It's unclear why LeGarrette Blount and Jonas Gray keep turning into the Monstars from Space Jam against the Colts, but unless their defensive front unearths some Secret Stuff, Indy might be playing with fire against the run.

But as two-back personnel becomes more situational rather than foundational, few defenses fear that kind of matchup. "Ranginess" and "mobility" have become the buzzwords you hear surrounding front-seven prospects, which are becoming smaller yet also more effective against the run. If an offense would rather load up and power a straight line down the field, most defenses would seem to welcome that change of pace.