Run Defense by Number of Backs, 2015
by Andrew Potter
If Monday's look at offensive rushing numbers by number of backs was instructive about the league's general trend away from multiple-back rushing sets, our look at the same numbers from the defensive side might shed some light on the reasons for that trend. As before, we're looking specifically at rushing attempts from the backfield, excluding quarterback runs and "wildcat" plays, and splitting the numbers into single- and multiple-back sets (with "back" defined as any non-quarterback in the backfield, regardless of the player's listed position).
Remember that this is from a defensive perspective, so negative DVOA numbers are a good thing (fewer yards and points allowed per play compared to an average team) -- which is good because there are plenty of negative numbers to discuss. Only three teams finished 2015 with a run defense in positive figures: Buffalo, San Diego, and Chicago. (Yes, even the historically inept 2015 New Orleans Saints defense had a negative run DVOA -- the Saints were 27th, at -2.4%.) The median run defense had a rating around -12.0%, while the median pass defense had a rating around 0.5%, because passing is generally more efficient than running on a per-play basis. You'll find a more detailed explanation of DVOA on our methods page.
As before, we'll start with the numbers before we get to the commentary:
|Run Defense by Number of Running Backs, 2015
|Defense||Pct 2+ RB||Rk||1 RB Rushes||2+ RB Rushes||Difference|
|Offense||Pct 2+ RB||Rk||1 RB Rushes||2+ RB Rushes||Difference|
On Monday, we noted that the number of rushing plays by running backs has declined substantially over the past nine years. Even though overall rushing numbers are only down around one play per team per game, the number of rushes by running baks has now declined by around 1,200 rushes per season, or around 10 percent since 2007. The offensive figures show it very clearly, but this trend is also evident in the defensive numbers.
Before 2015, there had always been at least one defense in the league that faced multiple-back sets on at least 50 percent of opponents' running plays. In 2015, no defense even faced multiple-back sets on 40 percent of those plays. The league-leading mark of 39.5 percent against Oakland would have ranked no higher than sixth in any previous year. At the other end of the table, Pittsburgh faced the lowest percentage of multiple-back rushes on record at 16.4 percent, and the lowest 12 figures have all come in the past two seasons. The raw numbers paint the same picture: the highest number of multiple-back rushes faced, 145, is down 34 percent from a year ago, while the lowest on record is now just 53 attempts faced, down 28 percent. Teams aren't only eschewing multiple-back formations against the teams who defend them best, they're reducing their use against everybody. The worst multiple-back defense in the league has only faced multiple backs on 28 percent of running plays in the past two seasons, after being above 40 percent every year before.
The reason for this is simple: even against teams who are bad at run defense, running is almost always less efficient per play than passing, and passing is generally more efficient out of single-back sets. Running is, if not an afterthought, certainly more of a complement to passing than a fully fledged offensive philosophy for the majority of teams, meaning even a bad run defense is not the liability it once was.
That does not, however, make the quality of a team's run defense irrelevant. Offenses still strive for balance, even if balance doesn't always mean what the network analyst claims it means. Balance, in the modern NFL, has nothing to do with 50-50 splits or even 60-40 splits or any specific target number. Balance is about mixing enough running into your offense to maximize the efficiency of the offense as a whole. It means controlling the game clock as well as the scoreboard, and "staying ahead of the chains" -- maintaining progress toward the next first down and, ultimately, toward points and wins. Sometimes that means a heavy dose of the random Patriots running back du jour plowing through the Colts defense, and sometimes it means throwing the ball on a dozen consecutive plays because Gang Green has eaten your offensive line.
Every team wants to be able to do just enough of the former to avoid the need for the latter, so even pass-first teams will look to manufacture a running game. This explains why teams that grade well against single-back runs are more likely to face a higher percentage of multiple-back runs, while teams that are mediocre against single-back runs rank middle-of-the-pack in percentage faced. Good single-back run defenses see opponents load up against them in an attempt to generate a running game, while there's no need to do so against mediocre single-back run defenses.
The one apparently illogical exception to this rule is Baltimore, who were top-ten against single-back sets and bottom-third against multiple backs, but still only ranked 27th in percentage of multiple-back runs faced. This might be vestigial, however, as the Ravens were excellent against multiple-back sets in 2014.
The Jets and Steelers are also exceptions, but for very good reason: both were top-ten against single-back sets, but were historically good against multiple-back sets and as a result ranked in the bottom three for percentage of multiple-back sets faced. We'll look at just how good these teams were shortly.
We saw in the offense article that teams are continuing to running fewer multiple-back plays year after year. The defensive table suggests that the quality of the defense against single-back sets has more bearing on the percentage faced than the quality of the defense against multiple-back sets. The consistent exceptions to the trend occur when the defense is very good against single-back sets and historically good against multiple-back sets.
When we say run defenses these days are historically good, that is not an exaggeration. Defenses, particularly the best defenses, are now devouring multiple-back sets like never before. Each of the top eight multiple-back run defense DVOA numbers have now come in the past two seasons, and all of the top ten such teams have come since 2012.
|Best Run Defenses vs. 2+ Backs, 2007-2015
Special mention must be made of last year's New York Jets. Their DVOA of -64.1% against two-backs sets is otherworldly, the defensive equivalent of the '06 Colts or the '07 Patriots offenses. They allowed only five rushing first downs all year to multiple-back sets, and three of those five first-down plays came with under 2 yards to go. The only rushing touchdown against them from a multiple-back set was a Tom Brady fourth-down sneak, which isn't counted in these numbers. Twenty-three of the 63 multi-back plays against them (37 percent) went for no gain or a loss. Buffalo, the second-ranked DVOA rushing offense, averaging 4.9 yards per carry from two-back sets, ran 24 two-back plays against the Jets ... gaining 52 yards and two first downs, for 2.2 yards per carry. The Jets were so excellent in this one area in 2015 that the gap between them and the second-placed Rams is about the same as the gap from the Rams to the tenth-placed Seahawks.
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That does not mean, however, that excellence in this category was confined to New York. Last year's fifth-best run defense against multiple-back sets was still good enough for seventh place since 2007, and would have led the league in any intervening year except 2014. It's not just the best teams who are enjoying unprecedented success against multiple-back sets either. Even the league-worst Chargers -- and they were absolutely dead last, with last year's 15.1% difference also the biggest gap between 32nd and 31st we've ever recorded -- would not have had the worst mark in any other season except 2010 (Arizona was league-worst that year at 10.7%, only slightly better than last year's Chargers), and are only the 12th-worst multiple-back run defense in the nine seasons since 2007. San Diego was the only team in the league last year to have a positive DVOA against runs from multiple-back sets, whereas every other year on record has seen at least five such teams.
It certainly looks as though offenses are naturally evolving away from multiple-back sets, and that change is being hastened by just how good defenses have become at stopping them. Granted, run defense DVOA is also improving against single-back formations, but nowhere near as dramatically as against multiple backs, and last year's leader in that category "only" has the second-best rating since 2007:
|Best Run Defenses vs. 1 Back, 2007-2015
Arizona had the best single-back rushing defense in the league last year, forcing more turnovers (five fumbles forced, four recovered, and a safety) than they allowed scoring plays (three). They ranked tenth by percentage of plays against two-back sets in large part because their divisional opponents are three of the nine offenses most likely to use those sets, but they were about equally effective by DVOA against either single- (-34.6%) or multiple-back sets (-27.8%).
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Last year's Jets also had one of the best single-back rushing defenses of the past nine years, in addition to the best-ever multiple-back run defense. Overlooked in some of the end-of-season coverage of the Saints' historic ineptitude was the fact that the 2015 Jets had the best overall run defense by DVOA since the 2000 Ravens, and the third-best of the DVOA era (1989-present) behind those Ravens and the 1991 Eagles. If the general trend is downward for rushing DVOA, last year's Jets defense is setting the pace.
As with multiple-back sets, it's not only the top teams who are historically good. The mean and median DVOA ratings against single-back sets are lower than ever before (remember, lower is a good thing for a defense), and more than a quarter of the league had a rating better than -20.0%. Whether it's a result of rule changes, restrictions on padded practice, coaching philosophies, or simply run defenders being easier to find than pass defenders, it's clear that run efficiency is continuing to decrease relative to that of the passing game. As long as rushing efficiency continues to decline, so too will rushing usage.
The NFL has changed a lot since 2007. Balance doesn't mean what it used to.