Football analytics will tell you that, generally speaking, NFL offenses have more success passing the ball than running the ball.

This makes a little intuitive sense: last year, NFL offenses averaged 4.1 yards per rush attempt, compared to an average 6.7 yards per pass attempt. Moreover, 34% of pass attempts resulted in a first down, compared to just 21% of rush attempts.

But how does that analysis change as offenses approach the end zone?

Conventional Football Wisdom Says Passing is Harder In the Red Zone

Last February, when the Vikings hired John DeFilippo as their offensive coordinator, DeFilippo explained that a core part of his offensive philosophy is creating explosive passing plays in the middle of the field, and then leaning more on your run game as you near the red zone:

The best traits of red zone teams in the National Football League is number one, your ability to run the football in the red zone. Because the safeties are going to be on you. There’s 22 guys in a tight space. Our backs are going to have to do a great a job of running through the unblocked players, [because] that’s the nature of NFL red zone football.

Passing is easier between the 20’s because the field is wide open: receivers can run any route at any depth and can stretch defenses vertically. Near the goal line, however, the back of the end zone is a boundary that eliminates deep routes and brings deep safeties closer to the ball. A shorter field means tighter coverage, tighter passing windows and tougher throws.

So the conventional wisdom makes some sense. But does it hold up to analytical scrutiny? To answer that question, let me explain one of my favorite metrics for offensive efficiency: “Expected Points Added,” or “EPA.”

What is EPA?

ESPN has a great breakdown of what EPA is and how it’s measured here, but the basic gist is EPA measures how much more likely a team is to score a touchdown or field goal before and after a play. It’s based on statistical analysis of every play over the past decade or more, and uses the down, distance, field position, time on the clock and other factors to determine how many points the average team in that exact position would be expected to score before and after a play.

So for example, if a team is facing 2nd-and-goal from the 10-yard line, and they throw a touchdown pass the next play, their expected points goes up from about 5 points to 7 points (from a pretty good shot at scoring a touchdown (or at least a field goal) to a guaranteed touchdown), for an EPA of +2. Conversely, throwing an interception on that same play would result in a negative EPA of about 7 points: -5 for scoring zero points when you had a good chance to score a touchdown, and another -2 points for giving your opponent the ball and thereby a decent opportunity to score themselves.

EPA tells us that teams generally get more expected points by passing the ball than by running the ball. Can it tell us how much teams should lean on their run game as they near the red zone and the field gets more constricted?

Methodology

Using Pro Football Reference’s game play finder, I pulled the EPA data for every pass or run play in 2017, and then grouped the data by the distance from the goal line. I then calculated the average run play EPA and average pass play EPA based on every distance from the goal line in the red zone, as well as from the 25, 30, 35, 40 and 45 yard lines and from midfield (about 6,000 plays in total, and a little over 200 plays per yard marker). I then ran a linear regression on the run EPA and pass EPA by distance, as well as the marginal difference in EPA between pass plays and run plays at every distance, to get an idea of how much harder it is to pass as the field shrinks and approaches the end zone boundary.

Findings: As Offenses Approach the Goal Line, the Marginal EPA of Passing Approaches Zero

Put more simply, the closer you get to the end zone, the less there is any advantage to passing over running. Here is a scatter plot of the data broken down by run play and pass play:

You can tell by looking at the orange dots high up on the chart that offenses generally are a lot more likely to put points up on the board when they pass the ball than when they run the ball: between the 20’s, the difference in average expected points added between passing the ball and running the ball is over a half-point per play. That’s a huge difference.

Conversely, when offenses enter the red zone, that passing advantage drops to just 0.2 expected points added per play. Generally it’s still better to pass than to run, but it’s no longer an enormous difference. And when offenses enter the ten yard line, the difference in average EPA drops to less than 0.1 expected points per play: a minor difference, and perhaps even negligible depending on the particular play call and match-up.

We can sum up all those findings in this next chart:

That trend line is the visualization of how big of an advantage passing the ball is compared to running the ball based on where the offense is. The closer the offense gets to the goal line, the less and less of an advantage there is in passing the ball. The data definitely seem to suggest that the conventional wisdom is right: passing the ball gets a lot harder as the offense approaches the end zone, and as a result, having a good run game becomes a lot more important in the red zone and near the goal line.

That said, there are some big limitations to the data.

It’s tempting to look at this chart and think that offenses should never (or almost never) run the ball, but we can’t draw any grand conclusions like that here. In statistics, your outputs can only ever be as good as your inputs, and here, our inputs are limited to two very broad buckets: pass plays and run plays.

Real football and real play-calling is a quite a bit more complicated than “pass the ball” or “run the ball.” In order to really evaluate NFL decision-making, we’d need to break down the play calls a lot further and answer a lot more questions: What routes were the receivers running? What was the pre-snap read? Was the run play zone or power? Inside or outside? How did the offense match up against the defense? What was the defensive play call?

Moreover, the EPA data pulled from Sports Reference differs slightly from the ESPN data and excludes important variables like time remaining and or home-field advantage.

Furthermore, when measuring the average EPA by distance from the goal line, certain samples of the data are skewed by a high number of outliers. For example, in 2017, teams at the 9 yard line had a lot more success running the ball than passing the ball. However, that’s likely due to the fact that eight interceptions were thrown last year from the 9 yard line, compared to only 2 from the 8 yard line. It seems unlikely that quarterbacks are that much more likely to throw interceptions from the 9 yard line than from the 8 yard line, so perhaps the data would be improved by looking beyond just 2017 and comparing previous years as well.

Partially as a result, the trend line is far from a perfect fit: in fact, only 27.5% of the difference in marginal EPA is explained by the distance from the goal line alone (in statistics parlance, the R2 value is only 0.2752).

Part of what makes football so great is it’s more art than science. It’s practically impossible to account for every detail, so we have to be modest with any conclusions we draw.

What conclusions can we draw?

Generally speaking, offenses have been more likely to put points on the board when they pass than when they run. That’s especially true in the middle of the field. That doesn’t mean offenses should never run the ball in the middle of the field, but perhaps offenses should think twice before leaning heavily on their ground game between the 20’s.

Conversely, passing the ball has only a slight advantage over running the ball in the red zone, and in goal-to-go situations, the difference is almost negligible. Teams shouldn’t be discouraged from passing the ball in the red zone, but as teams near the goal line, that’s when the run game and play sheet should really start to open up, particularly when other indicators — pre-snap reads, favorable match-ups, a schematic advantage — favor running the ball.