Advanced NFL Stats owes its start to an old water cooler debate: What's more important, offense or defense? Running or passing? A few years ago, I still had some statistical software left over from grad school loaded on my laptop, so I thought, "Hey, maybe these are questions that can be definitively answered." I tried to answer those questions with one of my original posts three years ago, What Makes Teams Win. When I read my older stuff, I sometimes want to cringe, but not with that one. It holds up very well, and it's well worth revisiting for newer readers, this time with more data. In this post, I'll do just that, focusing on the relative importance of running and passing.
When I was little, my dad taught me the inanity of the 'running leads to winning' fallacy. We'd watch a game on Sunday, and invariably we'd hear the announcers talk about how a team always wins when their star RB got at least 25 carries or so. They'd wax poetic about the noble nature of pure, old-fashioned, run-it-up-the-gut football. My dad would say, "Yeah, by that logic, teams should start kneeling in the first quarter. Kneeling leads to winning, right?"
But even in today's modern game, coaches continue to cling nostalgically to the run. We don't need to infer this from their play calling because as soon as they leave coaching for the broadcast booth, they spell out their running-leads-to-winning philosophies in plain English. Just last season, Brian Billick, who was the offensive coordinator for the most prolific passing offense in history, told the audience of NFL Network's Playbook NFC that the real secret to the Saints' success was their running game. Right.
It's possible to directly test the relative importance of running and passing toward the ultimate goal of winning using regression. Regression is one of those things that sounds really complicated but really isn't. If you have a relationship between two variables, say net passing efficiency and team win totals, you can plot the relationship on a graph, then draw a line that fits the relationship best. And with a little algebra we can use an equation to estimate the relationship.
If we wanted to estimate a team's win total using only its net offensive pass efficiency, I'd use: wins = 2.4 * pass efficiency - 6.6. For example, if a team threw for 7.0 net yards per attempt, that would work out to: 2.4 * 7 - 6.6 = 10.2 or about 10 wins.
Let's do the same thing with running efficiency.
In fact, if you look at only the points at or above the 10-win line, where the playoff teams typically reside, the graphs tell very different stories. Teams with 10 or more wins are no more likely to have strong running games than weak or even extremely weak running efficiency. In contrast, the teams with at least 10 wins are far more likely to have had above-average passing efficiency.
Comparing the two regression equations tells us a lot. For every yard of improvement in passing efficiency, a team can expect 2.4 additional wins. But for every yard of improvement in running efficiency, a team can only expect 1.1 additional wins.
When you have more than one variable that contributes to an outcome, its best to use multivariate regression. You can't visualize the regression model graphically, but you can produce an equation like the ones we see above. For the dependent variable, I'll use team win totals. For the estimator variables, I'll use efficiency stats for running, passing, turnovers, and penalties. This model is intended to be explanatory rather than predictive, so things like fumbles lost, which involve a large degree of randomness, are included.
There's one more thing I'm going to do before the regression itself. To truly compare the relative weights of the variables, I "normalized" them. This adjusts each variable so they're all on the same unit-less scale. Normalizing sets the mean of each variable to 0 and its standard deviation to 1. For example, a team that averages 4.8 yards per carry would be 1.5 standard deviations above average, and would have a normalized running efficiency of 1.5. Normalizing allows us to the answer the question, 'Which aspect of the game is it more important to excel in?"
The table below lists the result of the regression. Each estimator variable is listed along with its coefficient--its relative weight in terms of its importance in winning.
|Off Int Rate||-0.32|
|Def Int Rate||0.45|
|O Fum Lost Rate||-0.43|
|D Fum Lost Rate||0.25|
Here's how you can interpret the results. The constant means we start at 8 wins for a completely average team. For every standard deviation above average in passing efficiency, a team will win an additional 1.54 games. And for every standard deviation above average in running efficiency, a team win an additional 0.44 games.
Right away we can see that passing efficiency is the most important aspect of performance. At first glance it's three times as important than running efficiency. But that's before we factor in interception rate, which when added on top of passing efficiency makes passing over four times more important.
Fumbles (and fumbles lost) occur just over twice as often on pass plays than on run plays, usually due to a sack. So it's not clear how to apportion fumbles in the run-pass comparison. But even if fumbles strictly happened on run plays, it still wouldn't make running more than half as important as passing.
On the defensive side of the ball, we see the same general relationship. Stopping the pass is several times more important than stopping the run.
Theoretically, running should be just as important as passing due to game theoretic considerations. That's what is loosely meant by the adage "the run sets up the pass" and vice-versa. But despite this well-worn cliche, coaches and coordinators simply overdo the "setting up" part by over-playing the run on both sides of the ball. It's no different than a boxer who jabs too much.
It's not that running doesn't matter. It's just that passing is far more important. Running successfully can be critically important near the goal line, where the short field makes passing very difficult. Running also helps ice games in which a team has a lead, but that implies you need to somehow gain the lead in the first place.
Occasionally we do hear analysts on TV and in the newspaper columns refer to the NFL as a "passing league," but it's often meant as a criticism intended to chide teams for running running often enough. It's puzzling that in a sport watched and dissected by so many people, we continue to hear calls for teams to stick with the running game.
If I were advising a general manager, I'd tell him to largely forget about the run. Get a RB who's good at picking up blitzes or catching the ball. Never draft a RB in the first few rounds, and whatever you do, don't waste precious cap space (or payroll budget) on him. Get a quality QB at all costs. Assess your linemen on how well they pass block, and don't worry as much about their run blocking. Get lots of pass rushers on defense. Got a LB that's a great run stopper but can't play coverage? Trade him to some sucker team that cares that they only give up 3.8 yards per carry rather than 4.2 yards per carry. That's how you build a perennial playoff contender.