Aggressiveness Index 2017
by Aaron Schatz
Usually we wait until later in the offseason to bring out the Aggressiveness Index numbers, but we wanted to publish them a little earlier this season since they matter for this Sunday's Super Bowl matchup.
Football Outsiders introduced the concept of Aggressiveness Index 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. Although no NFL coach is as aggressive as the data suggests he should be, we discovered there is quite a wide range of fourth-down tendencies among coaches.
Aggressiveness Index numbers 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 Aggressiveness Index 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 regular season is included.
You may have read elsewhere that Doug Pederson went for it on fourth-and-1 more often than any other head coach in the league this season. There are actually two reasons for that. One reason is that Pederson was, in fact, really aggressive on fourth-and-1. He went for it on 61 percent of qualifying fourth-and-1s, more than any head coach other than Sean Payton. But the second reason is that no team got into fourth-and-1 as often as the Philadelphia Eagles. The Eagles ended up with 23 different fourth-and-1 opportunities that qualified for Aggressiveness Index. No other team had more than 17. Tampa Bay only had two.
Pederson doesn't actually end up No. 1 in Aggressiveness Index, which helps demonstrate how a couple of very rare fourth-down opportunities can heavily influence these numbers when we're looking at the small sample of just one season. Adam Gase is No. 1 instead, specifically because he decided to just throw caution into the wind with David Fales at quarterback in Week 17. Gase had Fales throwing on fourth-and-7 and fourth-and-3, both in the first quarter, and then on fourth-and-8 in the third quarter (losing by 13 points, which counts for AI). Without Week 14, Gase would have an AI of 1.14, which is still above average but not No. 1. Gase's aggressiveness is a bit of a shock since he was the most conservative coach in the league in his first season, going for it on just a single qualifying fourth down in 2016.
Jack Del Rio is also ahead of Pederson. He was aggressive on fourth-and-short, though not quite as aggressive as Pederson. However, he passes Pederson in AI because the Raiders had Marquette King run a fake punt on fourth-and-11 from his own 30.
Here are the full Aggressiveness Index results. Each situation is listed with the number of times the coach went for it and the number of opportunities, the rate, and then the expected number of times an average coach would go for it given the down, distance, score, and location on the field.
|2017 Aggressiveness Index|
Some of these results further show how one season is just a small sample size of fourth downs. Gase is not the only head coach to make a big change from 2016 to 2017. John Harbaugh, usually among the most aggressive head coaches, comes out in the bottom half. Mike Zimmer drops from ninth to last. Jim Caldwell had also been very aggressive the previous couple of seasons.
With that in mind, we may look at including a three-year rolling average of AI in Football Outsiders Almanac 2018 instead of just the single-season number. We'll have more on Aggressiveness Index later in the offseason, including updated career numbers that will add in 2017 as well as 1986-1988.