There aren’t many knocks on Kyle Shanahan as a head coach. Shanahan does an excellent job of looking at the game from a macro level and putting his team in the best position to succeed.
If you were making a list of where Shanahan could improve as a coach, you wouldn’t get far before mentioning his decision-making on fourth down. For a coach who’s revered as the brightest offensive mind in football — a reputation Shanahan’s earned — there are a couple of times a game that leaves you wondering why he didn’t go for it.
The 49ers boast one of the most prolific offenses in the NFL. That’s been the case for a few seasons, but the Niners went to another level after acquiring Christian McCaffrey. Despite having a quarterback he was confident in and weapons surrounding Brock Purdy, Shanahan’s aggressiveness on fourth downs didn’t change.
In last year’s Football Outsiders Aggressiveness Index rankings, Kyle went for it on fourth downs at a 16 percent clip, which was below league average. This year, Shanahan remained subpar as his go-for-it rate dropped to 13.5 percent.
One thing to note with the Aggressiveness Index is that the Football Outsiders formula has undergone regular change, so direct AI number comparisons won’t be applicable.
Last year there was a re-calibration to adjust for the fact that coaches are much more willing to go for it on 4th down than, say, the 2015 season. Let them explain it better than I can:
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.
You may remember that last year we re-did all the baselines for Aggressiveness Index. Head coaches in the NFL had become so much more aggressive since 2018 that the leaguewide Aggressiveness Index was up to 1.90 in 2021 and not a single head coach in the league came in below 1.0 that season. Based on changes in coach tendencies since 2018, our new baselines expect coaches to go for it more often on fourth-and-short, near the goal line, and near midfield.
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 the regular season is included.
If we reference RBSDM’s 4th down aggressiveness metric, Shanahan ranked 26th in “go for it when he should” situations based on win probability gain, and within the win probably parameters of 20-100 percent. There are other exclusions included in Football Outsiders metrics that help explain the discrepancy in the two statistics.
You can see each 4th down decision here from 2022, and it has the win probability boost along with what part of the game it happened.
From a decision-making standpoint, Week 3 against the Broncos was overwhelmingly bad. But that, of course, was Jimmy Garoppolo’s first start and against, at the time, a quality defense.
Coincidentally, the other game that was the lowest was Purdy’s first start against the Dolphins. The decision to go for it on fourth down, where Purdy threw an interception on a deep pass to Aiyuk, actually was a net positive, since they gained field position.
Shanahan’s failing to go for it on fourth down isn’t anything new. He ranked 28th in 2020, but when you look at whom he had as a quarterback, that isn’t surprising. But even with a veteran roster when he was 13-3 in 2019, Shanahan found himself at 28th again.
The most aggressive coach in the NFL was Nick Sirianni, who relied heavily on quarterback sneaks in short-yardage situations. It’ll be interesting to see if Shanahan evolves with a full season of Trey Lance under center.