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Trending the NFL: Rediscovering The Nature Of Football

In the conclusion to my three-part miniseries covering the relevant statistics in football, I ended up (as I often do) in a place that I didn't anticipate from the outset: philosophy. I'll be taking a deeper look into the discrepancies between statistics that I discovered in the previous post to discern what exactly it means for football.

Mark J. Rebilas-USA TODAY Sports

Okay, if you're just joining us for the final part in this series, you can read the first two posts (and everything else related to my ranking system, "Crunching The Numbers") through this hub. They cover a lot of background that I'll touch up on here, but the previous posts have a more in-depth analysis that I recommend you look at if you're a stat nerd like I am.

When I began my project of tracking and trending NFL statistics in 2013, it was only for the purpose of analyzing the metrics I used for Crunching The Numbers. I ended up learning more than I anticipated, and the same held true for this year. In hindsight, I probably should have seen it coming this time around, but I guess that one's on me.

Before getting into the meat and potatoes of this post, I'll offer the disclaimer that I'll be making observations based off of numbers. These numbers are called correlation coefficients, which were found through a simple linear regression analysis. The basics behind them are laid out below (for a deeper explanation, check out the first post in this miniseries):

  • All numbers associated with each statistic are correlation coefficients, and they quantify whether or not that statistic has any sort of relationship to winning
  • positive number implies a positive relationship (for example, more points scored = more games won)
  • negative number implies a negative relationship (for example, fewer points allowed = moregames won)
  • In order to have 95% confidence that a number is not coincidence, the value of the number must be at least 1.00
  • The maximum value a number can have is 2.8623

Okay, now that we have that covered, I'm just going to dive right into the content here and discuss a phenomenon in football that I have simply and unimaginatively entitled, "The Big Gap."

The Big Gap

Let's start things off with a thought experiment. Picture two fictional and evenly-matched teams. The nameless running back is carrying the ball and has reached the second level. The only remaining opposition is a single, nameless safety. The question is: what happens next?

After reading that question, take a note of the first thing that came to your mind. We'll get back to that in a minute, but for now let's table the hippie-dippie stuff and look at some cold, hard numbers (this will make sense, I promise):

Statistic Offensive Correlation Defensive Correlation Difference
Points 2.34 -2.07 0.26
Rushing Attempts/Game 1.43 -1.78 -0.34
Rushing Play % 1.06 -1.90 -0.84
Incompletions/Game -1.12 1.65 -0.53
Yards/Pass Attempt 1.90 -1.45 0.45
Sacks -1.58 0.91 0.67
Passer Rating 2.03 -1.80 0.24
Passing Play % -1.06 1.90 -0.84
Interceptions/Game -1.83 1.24 0.58
Interception % -1.98 1.14 0.83
Turnovers -1.81 1.16 0.65

The above table shows the statistics that correlate with winning that are "shared" by both the offense and defense. The "difference" column is the absolute value of the defensive correlation subtracted from the absolute value of the offensive correlation. Notice anything interesting? Out of the eleven statistics in that list, only four have a stronger connection to defense than offense. This indicates that the offense has a much higher influence on winning when everything else is equal. Take interceptions per game for example, where the offense holds a noticeable 0.58 edge. This implies that if one team throws five fewer interceptions than the league average and a second team forces five more, the first team will still win more games than the second, even though this seems counterintuitive.

Now let's go back to our thought experiment. What did you say happened next? Did you say that the running back got tackled? That's the first thing that came to my mind when I envisioned the scenario. But maybe you thought he broke the tackle or juked guy out and took it to the house. All of those outcomes are certainly plausible and entirely valid.

But are they equal?

That is the question at the heart of all of this and the driving force behind the Big Gap. Does a completed tackle offer the same value to the defense that a missed tackle provides to the offense? Does a forced sack offer the same value to the defense that an allowed sack removes from the offense? What about turnovers? Passer rating? Points?

Common sense would dictate that the relationships should be symmetrical. An offense loses value when it allows sacks, so the defense should be able to find the same amount of value when it forces them. The same should be able to be said for everything. It creates a balance, like good versus evil, ying versus yang.


And yet, the numbers above scream the opposite. They suggest that the offense far and away has more to gain - and lose - by performing well in these metrics. An offensive giveaway hurts the team more than a defensive takeaway helps. A quarterback's passer rating helps the team more than the defense's ability to limit the opposing quarterback's production.

But why is this true? Why does the offense have such a larger impact? Why isn't it equal?

My best guess is that, from a purely logical perspective, the offense wins the game. You need to score points to win football games - a lot of points in the modern age. If both team's defenses took a vacation and it was just the offense out there, more likely than not you would have a winner at the end of the game. If the opposite happened, it would be a tie because the score would be 0-0. Because of this, all of the pressure is on the offense to overcome the defense. This would explain the Big Gap.

So is defense dead then? Are surgical passing attacks going to turn the NFL into Arena Football, where the last team to have possession wins? Is the old adage, "defense wins championships" simply untrue?

Not exactly. In fact, you could make an argument that defense still wins championships. Look at the four statistics where defense has an edge over the offense. Three of them (rushing attempts per game, rushing play percentage, and passing play percentage) have nothing to do with the limiting the offense - they are all about play selection. In other words, coaching. The offense may be under pressure to overcome the defense, but the defense is under pressure to overcome the coaches. More specifically, the defense's main purpose is to force the opposing coaches to abandon the run game. This is why defense wins championships, because in the NFL Playoffs, where the talent and skill is basically equal among teams, the winners are more often than not decided in the meeting room when the game plan is created.

Bringing It All Together

The title of this post is about rediscovering football. So if we look back on the observations made and the numbers analyzed, what do we have? What we have is evidence that allows us to make a generalized inference about the true dynamic of the game and the intertwined relationship between offense, defense, and coaching. In a way, this is enough to create a foundation to building a successful football team. You can experiment with schemes, plays, and formations, but at the end of the day you're left with two questions:

Is my offense successfully overcoming the opposing defense?

Is my defense imposing my will on the opposing coaches?

Those two questions encapsulate the sport and might even be able to be applied to individual games. It's beautiful, actually, how simplistically an undeniably complicated game can be defined. And in my book, being able to take something complex and define it in a simple way is discovering the true nature of it. But of course, as with all things complicated, there is never a truly black-and-white summary. There is no one correct explanation.

So, what say you?

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