Thoughts on the Apparent Unimportance of Run Defense

John Morgan of the Seahawks blog asked me recently about why run defense appears relatively less important in terms of winning than do other facets of the game. John writes:

You state defensive rushing yards per attempt allowed is the least important component to winning, but I wonder if that factors in game situation. Losing teams are likely to reduce their yards per attempt allowed when winning teams are running out the clock.

John makes a good point, and indeed the team-stat regression model I used when I made that conclusion did not take game situation into account. John goes on to point out that teams that are already behind may face a large number of predictable run-out-the-clock runs, which would make their run defense appear better. Plus, the game theory aspects of running and passing should enable a good run defense to make stopping the pass easier.

I think this is an interesting point, and I soon should be able to test how much late-game runs affect a team’s overall defensive efficiency after some improvements to my play-by-play database. A preliminary look indicates it probably doesn’t make much of a difference. Still, I think John raises good points about the game theory aspect and predictability.

In theory, good a run defense should make a pass defense better. And the stats suggest it does. The correlation between defensive running efficiency and passing efficiency is 0.20. Some of that correlation has to do with the fact that superior defensive athletes are superior against both the run and the pass. But some of it should also be due to the game theory aspect.

(In comparison, offensive running and passing efficiency correlate at 0.13. I think the difference is that there is a lot more variance in offensive passing than in other facets due to the focus on a single player’s ability. The quarterback’s contribution is so critical to passing in ways that aren’t applicable to the other aspects.)

According to game theory principals, defensive running and passing would only be equally important if offenses and defenses were operating at the game equilibrium point-- that is, they’re playing the optimum mix of passing and running. But I think they might not be.

My theory is that this may be why run defense appears so unimportant. Say teams are not operating at the game equilibrium, and passing is, on balance, a more lucrative strategy than running. In other words, there really is a considerable passing premium where the payoff for a pass is generally higher than a run, all things considered.

Having a good run defense would therefore be somewhat self-defeating. Take the 2007 Vikings defense that gave up only 3.1 yards per run (good) but 7.0 yards per pass (bad). Facing such a solid run defense, a good offensive coordinator is forced to pass more…which would be a far more effective thing to do in the first place, especially against a relatively weak pass defense. A team like the 2007 Vikings would essentially be forcing their opponent to unwittingly play a more efficient and effective strategy, all the while exploiting their own weakness.

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5 Responses to “Thoughts on the Apparent Unimportance of Run Defense”

  1. Unknown says:

    Good discussion. I'll be really interested to see what results can be found when game situation is considered. Intuitively, it seems like it's critical for a team to be able to play good pass D when they have the lead. In terms of Run D, it just seems like you need to be decent at it. That is, I'd assume teams with very bad run defense in close game situations don't win much. Once you're average or better, maybe it doesn't make as much difference? Anyway, I look forward to seeing what you come up with.

  2. PackerNation says:

    I have a very simple explanation for this.

    In the NFL, it's all about PASSING the ball effectively. Whoever moves the ball through the air most effectively wins the game most of the time.

    But if you aren't stopping the run, you're not going to have as many quality opportunities to make the kind of big plays in the passing game that tilts the balance. You're not going to have teams in 3rd and long, you're not going to be able to get your sub-packages on the field, you're not going to be able to apply all-out pressure as much.

    So you have to stop the run to give your defense an opportunity to make some plays in the passing game. Once you've done that, then you actually need to MAKE PLAYS in the passing game.

    The Vikings are an unusual case because they can win the ground battle on both sides of the ball but they're at a disadvantage in the air war.

  3. Jason says:

    These days, though, stopping the run doesn't seem like the only way to force teams into third-and-longs. A lot of teams use those little 3- and 4-yard passes on early downs as substitutes for their running games.

    As a Vikings fan, I've enjoyed watching our impregnable run defense for the last few years, but I'd gladly give up some of it for better pass defense. I've advocated trading Pat Williams for years.

  4. Al says:

    "Game situation" may have an impact beyond late-game runs.

    Houston Texans fan suffered through a number of years when it would have been reasonable to call the whole second half "late-game." When you're trailing by 3 touchdowns, the opposition is going to defend pass first. This will inflate your run (per attempt) stats, and deflate their run defense stats. The general rule is, your offense will normally produce better stats doing the unexpected.

    This concept may well play out on a smaller scale throughout the game -- especially on 3rd downs (but sometimes on 2nd and long as well). The Texans faced a lot of 3rd and long, and 3rd and VERY long, situations. Since the opposing defense was defending pass first, I would guess that our yards/rush were inflated by these situations (especially draw plays).

    On the other hand, the opposition typically faced a lot of 3rd and short, and 3rd and VERY short, situations. Since our run defense was not good, in those situations the opposing team tended to do the expected; they ran. They only picked up one or two yards, but they usually got the first down. So, it tended to make our run defense look better and the opposition rushing offense look worse. (Note also how the situation impacts the TYPE of run play. They run plays with a high probability of gaining one or two yards and little probability of gaining 20 yards. No draw plays here.)

    First down runs when the game is still close may be the closest to a pure measure?? I' be curious to see what those numbers look like -- and how they compare with the full game stats.

    I'm rushing, so the above isn't as clear as I'd like it to be.

  5. Brian Burke says:

    Al-I get you. Good point.

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