How Does the Speed of NFL Defenses Affect Production?

The Atlanta Falcons did a lot of things right last year that the rest of the National Football League should be taking notice of.

We can all be forgiven for not predicting the overhaul of a franchise mired in mediocrity until a run to Super Bowl LI marked the dawn of head coach Dan Quinn’s era in A-Town. What everyone focused on in the home stretch of the season, however, was the explosive, first-ranked offense in the league.

All the while, a young and talented defense was taking off at light speed and becoming one of the most promising units in the NFL.

Aside from a historic collapse in the title game, the Falcons’ defensive unit gelled down the stretch and turned into a fearsome force. After the Week 12 bye, Atlanta allowed first downs on just 34.42 percent of their plays, converted interceptions on 2.73 percent of passes, and sacked opposing quarterbacks well over 5.00 percent of the time.

Their supposed secret ingredient: speed; pure, unadulterated velocity in their defensive players.

Is this truly the key to unlocking great defensive play in the modern NFL?

I Wanna Go Fast

The Falcons proudly declared their speed-based strategy the hallmark of this team from the moment Dan Quinn stepped into the Flowery Branch team facility a few years ago. According to general manager Thomas Dimitroff, in early meetings as they hashed out what the tone of the roster would be: “Everyone was emphasizing speed, speed, speed. This was going to be one of the fastest teams that any of us would ever put together.”

They delivered on those promises of high-octane aggression when they picked players like defensive tackle Ra'Shede Hageman and edge rusher Vic Beasley in 2014 and 2015, and built on them even further with the 2016 NFL Draft selections of safety Keanu Neal, along with linebackers Deion Jones and De'Vondre Campbell to shore up this defensive diesel engine.

In the run-up to the Super Bowl, even New England Patriots head coach Bill Belichick acknowledged that this Falcons team might be a tough opponent because “they look like they're faster than almost every team they play. ... They have a lot of fast guys defensively. They close up space very quickly.”

When we pull together the snap-weighted Speed Score of every team in the league, Atlanta does show up as one of the most explosive defensive units in the NFL. The Falcons' 101.31 weighted Speed Score was the ninth-highest in the NFL this year, but they actually weren’t a productive defense by Net Expected Points (NEP) -- numberFire’s signature metric.

For context, Speed Score is a metric that adjusts a player’s 40-yard dash time for their weight (a big guy running fast is moving more mass than a small guy running the same time), and I averaged each player’s Speed Score by how many snaps they played to figure out each team’s total defensive speed impact. NEP describes the contribution a play (or player) makes to their team’s chances of scoring. By adding down-and-distance value to standard box score information, we can see just how much each play and each team as a whole influence the outcome of games. For more info on NEP, check out our glossary.

The Falcons ranked 11th-lowest in Adjusted Defensive Passing NEP per play and last in Adjusted Defensive Rushing NEP per play this year, a far cry from the “speed is king” manifesto they proclaimed. For all the talk of this quality being the key to defense for Atlanta, it seems like there was no real payoff in 2016.

Does speed really not matter on the defensive side of the ball?

Terminal Velocity

By using correlation, we can test whether or not there is any relationship between a defensive unit’s success on the stopwatch and their production on the field.

Essentially, the closer the value of a correlation is to 1.0 or -1.0, the stronger the relationship between the two data sets is. On the other hand, if it falls near 0, it means there is little to no relationship.

I broke apart the defense and Adjusted Defensive NEP per play into each of their component parts and compared each position group to each facet of defensive value production. In the former category, we looked at the defense as a whole, defensive line, edge rushers, (off-ball) linebackers, and defensive backs. For values, we looked at total Adjusted Defensive NEP per play and each of the passing and rushing variants on this metric.

The table below depicts these correlations. We should also note that a relationship towards the negative is a good thing here; Defensive NEP describes how much value a defense allows to an offense, so a negative total means that higher speed leads to less value allowed.

The strongest correlations across the board land in the relationship of a position group’s Speed Score to Adjusted Defensive Rushing NEP per play, with the only significant relationships being shown for defensive backs, edge rushers, and linebackers. This data seems to indicate that there is no true relationship of quality of passing defense to the raw speed of its players, possibly due to the effectiveness of zone defenses that rely less on speedy cornerbacks and more on player awareness and read-and-react ability.

Another interesting correlation to note here is that the faster an edge rusher was, the less effective their defense was against the run. Speed rushers like Vic Beasley are aiming to blow by running backs and level the quarterback, but meaty guys like Terrell Suggs are in position to set the edge and rip down rushers.

Finally, we get to the two points that help to confirm the Falcons’ rationale in drafting Neal, Jones, and Campbell last year with three of their top picks: defensive backs and -- to an even greater extent -- linebackers excel against the run the faster they are. This makes sense: for the former, they play deeper off the line and away from the hash marks, so they have to come all the way back to deliver a hit on the runner. If they can’t generate enough speed to get to the ball, they won’t be able to contribute.

For the latter, they also need to be able to flow and chase to the point of attack, intercepting the ball-carrier before they get to the third level of the defense. The faster they run, the better the chance is that they cut off an open-field breakaway before it begins. This whopping -0.50 correlation indicates a pretty strong relationship between linebacker speed and the effectiveness of a defensive unit against the run.

For those of you who think the Falcons’ high-octane approach tired them out in the Super Bowl, it’s entirely possible that Jones' and Campbell’s speed is what kept them in it in the first place. Remember, too, Jones was thought about as a possible safety coming out, so it’s possible that those fast, hard-hitting college safeties should be used in the second-level in the NFL, helping to add coverage value through range and run-stopping production by flowing bodies to the play.

Velocity is a precious commodity in the modern NFL, and players that can keep their feet on the pedal are like a 1964 Ferrari: priceless.