The battle between run blockers on the offensive line and run stoppers on defense defined the NFL for decades. But, in 1994, the league changed its rules to incentivize passing and turned football from a sport largely decided in the trenches to one decided in the air. Along the way, the league that averaged 18.7 points per team game in 1993 morphed into one averaging 24.8 points per team game last season — an all-time record.
But despite passing’s modern proliferation, the art of run stopping is far from dead. NFL teams still value run defense, and many continue to invest in interior defenders skilled at closing off running lanes. Washington interior defensive lineman Daron Payne was the 13th overall pick of the 2018 draft, and the New York Jets took Quinnen Williams third overall in 2019. Each are skilled, big men who can play different positions along the line and possess pass-rushing ability,1 but both are primarily intended to help their teams defend the run.2 Clearly, teams believe stopping the run is important, or they wouldn’t spend premium picks to acquire players adept at that skill.
Given this belief, we were curious which teams were best at stopping the opposing ball carrier, and how much that actually matters. Specifically, we wanted to measure if a good interior run defense contributes to winning football games. Does interior run defense impact the number of points that a team allows? Does a stout interior line encourage the other team to pass more — and, by extension, gain more yards?
To try and quantify run defense, we built off of the work of ESPN analyst Brian Burke, who introduced the “run stop win rate” metric last year. His metric is based on NFL player-tracking data from 2017 to 2019, and is calculated by using “angles, distances and speeds throughout the execution of a play to tell who is blocking whom and to determine whether the defender was able to meaningfully beat the block (or blocks in the case of a double-team)” on designed running plays.
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“Run stop wins” is a promising metric. Burke reports that, on average, the opponent’s rushing effectiveness decreases as the number of a team’s run stop wins on a play increases, indicating a well-calibrated measure of defensive performance. Our new metric takes the metric developed by Burke and the ESPN analytics team, and adjusts for two items over the course of a season: the volume of rush snaps each interior lineman faced, and the types of “techniques” he played. Techniques are essentially the roles the lineman was asked to perform along the defensive line. For instance, a “zero technique” means the lineman will set himself directly over the center, while a “three technique” means he will set up somewhere in the gap between the guard and the tackle.
We adjust for techniques played because an interior defender lined up directly over the center (zero technique) tends to earn more run stop wins per 100 snaps than the players asked to line up directly over the guard (two technique) or the tackle (four technique).3 And since snap volume has a big influence on the number of run stop wins a player can expect to earn, we adjust for that, too. After finding the expected run stop wins for each technique, we aggregated expected run wins by player, calculated each defender’s wins above or below expected, and then summed those up by team.
We call our new metric “run stop wins over expected” (RSWOE). According to it, the New York Jets had the best interior run defense in the NFL in 2020 — and it wasn’t even close. Led by Williams’s 36.9 RSWOE, which is the highest of any interior lineman in a season since 2017 (when player-tracking began), the Jets lapped the field, adding over twice as many run wins as the second-place Los Angeles Rams.
At the other end of the spectrum are the Minnesota Vikings, sitting almost 200 RSWOE behind the Jets. Shamar Stephen (-50.7) and Jaleel Johnson (-28.5) led the way in defensive-run futility for Minnesota, with Stephen’s incredible 50.7 run wins under expected ranking as the worst in an NFL season since 2017. Indeed, Stephen’s poor play against the run has been remarkable in its consistency: Stephen owns three of the 16 worst player seasons of the past four years (according to RSWOE), making him by far the league’s biggest liability against the run among interior linemen.4
One important note here, though: There isn’t a clear pattern that emerges between RSWOE and many other measures of defensive performance. When we look at its correlation with defensive points allowed or team scoring margin, for instance, virtually no relationship exists. Being good at stopping the run doesn’t appear to help defenses prevent offenses from scoring, and being bad doesn’t appear to hurt in that effort.
Digging deeper, a team’s RSWOE holds a weak but positive correlation with the expected points added that it allows per play. And since negative EPA per play is good for a defense, a positive relationship between the two indicates that the higher the RSWOE, the less efficient the defense is overall. We see a similar story with defensive success rate, though it has an even stronger correlation in the wrong direction. Defensive success rate measures the share of plays in which a defense prevents an offense from gaining positive expected points added. (For instance, a defense holding an offense to a 2-yard gain on second and 5 would be considered a success by this metric.) Higher numbers are better for the defense, so a negative correlation means we still find that the stronger the interior run defense, the worse the overall defensive performance.
|metric||corr with wins over expected|
|1st down rush %||0.08|
|3rd down conv. %||0.01|
|Def. success rate||-0.17|
|Rush yards % of offense||-0.26|
Meanwhile, the strongest correlation tested suggests that the more dominant the interior run defense, the more an opponent will drop back to pass — and the less it will try to run.5 In some ways, this is the expected result: Rational playcallers are avoiding strong interior lines by passing more. Yet defenses also tend to suffer when they funnel more of the opposing offense’s plays into the passing game, since passing the ball remains more efficient than running it.
That takeaway may upset teams that have invested heavily in run stopping interior linemen. But for those teams, it’s worth considering if enticing your opponent to run its most efficient play type against you is a suboptimal strategy. Unless your defense is dominant in all facets of the game, incentivizing your opponent to run more — and pass less — will likely be a better approach. Because ultimately, in a league that is structured to reward teams that throw early and often, daring your opponent to pass is probably a recipe for disappointing results.
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