NFL Offseason – The debate over fourth downs is over, and the analytics have won.
Oh, it may not quite seem that way when you watch commentary on TV. There are still old school football people attacking coaches for being too aggressive, for “chasing points” or alternately “leaving points on the board,” for not “playing the percentages” (when they are in fact doing just that). You’ll still hear stuff like this on sports radio, attacking “the freaking nerds.”
It doesn’t matter. Head coaches still might not be quite as aggressive as the analytics would suggest, but they are much more aggressive on fourth downs compared to just four seasons ago. The analytics won the argument, and things have changed.
And because we’ve won the argument, this year Football Outsiders has to change our Aggressiveness Index metric which measures how often coaches go for it on fourth down compared to the league average. What constitutes “league average” has changed so dramatically that the old numbers don’t quite make sense now.
Football Outsiders introduced the concept of Aggressiveness Index way back in Pro Football Prospectus 2006. The goal was to find a way to rank coaches based on their tendencies on fourth downs in a manner that was easy to understand but accounted for the different rates at which the average coach will choose to “go for it” in different situations. There are other methodologies now for measuring fourth-down aggressiveness, mostly based on win probability analysis: for example, the EdjSports head coach rankings or results spit out by Ben Baldwin’s fourth-down simulator. Each methodology will have small differences in how it ranks the coaches, but Aggressiveness Index differs from the others by measuring coaches not against what they should do but against the actual decisions made by coaches themselves.
Aggressiveness Index numbers were designed to center around 1.0 and generally describe how much more (or less) likely each coach is to go for it on fourth down compared to his peers; for example, a coach with 1.20 AI is roughly 20 percent more likely to go for it than an average coach in equivalent situations.
The problem we’re now having is that when we compare current coaches to historical averages, AI numbers no longer center around 1.0. The leaguewide Aggressiveness Index in 2021 was up to 1.90. In 2020, only two head coaches came in with an AI below 1.0: Vic Fangio and Brian Flores. This season, not a single head coach in the league came in below 1.0. Using the original AI baselines, Joe Judge was the lowest head coach in the league at 1.03.
|NFL (Old) Aggressiveness Index, 2014-2021|
The Aggressiveness Index, by the way, excludes obvious catch-up situations: third quarter, trailing by 15 or more points; fourth quarter, trailing by nine or more points; and in the last five minutes of the game, trailing by any amount. It also excludes the last 10 seconds of the first half, and it adjusts for when a play doesn’t actually record as fourth-and-short because of one of those bogus delay of game penalties that moves the punter back five yards. Only the regular season is included.
Obviously, there’s going to be a problem with a metric that is designed to average around 1.0 if every single coach is coming out above 1.0. The average decision-making on fourth downs has changed dramatically since 2018. Our baselines have to change also.
Before we introduce the new numbers with the new baselines, let’s take a step back and look at how much things have changed since 2018. These charts will include all fourth downs, including those in obvious catch-up situations.
First, raw go-for-it rates show how things clearly changed in 2018. The league go-for-it rate, including in late-game catch-up situations, hovered around 12% for three decades. Then it started going up four years ago. It’s now above 20%.
Go-for-it rates have changed at pretty much every distance, but the difference is clearest in the shortest yardage: fourth-and-1 and fourth-and-2.
Where are coaches going for it more often? Not all over the field. There are two places where coaches are going for it more often. First, they go for it more often within 10 yards of the goal line. Second, they go for it more often at midfield, roughly between the 35-yard lines. The rest of the territory shows go-for-it rates not too different from those we saw historically from 1983 through 2017.
Put these charts together, and you can see where these three situations are driving the change in head coach aggression. In short yardage, near the goal line, or between the 35s, attempts on fourth down are way up. The rest of the time, they’re up very slightly.
And so, that’s where we’ve changed our baselines. Coaches are now expected to go for it more often on fourth-and-short, more often near the goal line, and more often near midfield. The average Aggressiveness Index for the period 2018-2021 is back to 1.0.
Here are the full Aggressiveness Index results for 2021, based on the new AI baselines representing 2018-2021. The identity of the most aggressive head coach in the league will not surprise you.
With the old baselines, Brandon Staley had an AI of 3.21. This would not be a record; John Harbaugh was at an astonishing 3.95 in 2019. But still, that’s pretty high. With the new baselines, Staley leads the league at 2.08. He’s the only coach to go for it more than twice as often as the expectation, but that’s the new, higher set of expectations based solely on the last four seasons.
Some additional notes on this year’s Aggressiveness Index:
- Frank Reich ranking only 11th is a bit of a surprise because he went for it so often on fourth down, but he went for it so often because he was in fourth-and-short so often. The Colts had the most qualifying fourth-and-1 opportunities, going for it on 16 out of 20.
- We’re still not at the point where any coach goes for it on every qualifying fourth-and-1, but we got close. Nick Sirianni (6 of 7), Matt LaFleur (7 of 8), and the combined Jacksonville coaches Urban Meyer and Darrell Bevell (6 of 7) all went for it on every qualifying fourth-and-1 but one.
- Pete Carroll was at the bottom of the league overall and specifically on fourth-and-1, going for it on just three of 10 qualifying fourth-and-1 opportunities.
- Staley and Bruce Arians led the league with 12 qualifying fourth-and-2s. Staley went on seven on those, Arians on only two.
Here’s a look at the top 10 coaches since 2018 in the new Aggressiveness Index:
And a look at the bottom 10 coaches since 2018:
Note that we’ll still track both versions of Aggressiveness Index so that we can compare current head coaches to those of the past. But when we’re just comparing current head coaches to each other, we’ll use the new Aggressiveness Index so that we don’t live in some Lake Wobegon NFL where every head coach is above average.
Thanks to Jim Armstrong, who came up with the idea of Aggressiveness Index and computes it for every season.