Most of the optimistic projections about the Falcons (including mine) go something like this:
They still have Matt Ryan and Julio Jones in their primes. The o-line was adequate last year once the injuries subsided and a five-man unit coalesced. The secondary was good last season but had to cover all day with no pass rush; Vic Beasley definitely helps that and Adrian Clayborn can if he stays healthy. New coach Dan Quinn will avoid Mike Smith’s late-game strategic blunders and work his guru magic on the defense like Smith never could.
It’s that last part that Football Outsiders wanted to check. The advanced stats website (via its ESPN Insider platform) studied how first-year coaches hired from 1990 through 2014 with clearly offensive or defensive backgrounds were able to improve the team’s performance on that side of the ball. They measured this using defense-adjusted value over average, or DVOA. The metric is one that is used in some form by most if not all NFL teams in their self-evaluations and is explained in detail here.
FO concluded that teams with first-year “defensive” head coaches improved their defensive DVOA by an average of 1.4 percent while teams with “offensive” head coaches improved their DVOA by an average of 3.4 percent. The gap in DVOA improvement for defensive and offensive head coaches decreases for each season after Year 1 until the average difference is about one percent in Year 3.
Wrote Football Outsiders' Sterling Xie:
Offensive coaches tend to start from a lower baseline and see more immediate improvements, but it's questionable whether the average defensive coach has any Year 1 impact at all. We've previously found that defense is less consistent than offense from year to year, so that tiny minus-1.9 percent "improvement" might simply be noise. Again, we can turn to Atlanta and Chicago for evidence of this. Quinn and (John) Fox both had the task of overhauling the previous regime's defensive personnel to find better fits for their new systems. But there's only so much that can be done in a single offseason, which has left lots of misfit pieces such as the Bears' Jared Allen and Willie Young, and the Falcons' Tyson Jackson and Robert Alford lingering in the wrong scheme. Unsurprisingly our projections in Football Outsiders Almanac 2015 have the Falcons and Bears finishing 29th and 30th, respectively, in defensive DVOA this season.
The Falcons ranked last in defensive DVOA last season so 29th would be an improvement. But correlation does not necessarily imply causation and there potentially is lots of noise in the Football Outsiders analysis.
When a team changes coaches (or even when they don’t), lots of factors vary from season-to-season: roster turnover, returning players who get better or worse, more or less injuries, tougher or easier schedules, more or less luck, etc. Also when a team hires a new coach, it is almost always because the team was bad the previous season and so improvement in Year 1 could be improvement that would have happened regardless of whether a team changes coaches. It's easier for a very bad team to get a little better than for a very good team to get even better.
But if the history of coaching hires is an indication, then perhaps expectations for defensive improvement in Quinn’s first season should be tempered. Or maybe the Falcons will be one of the teams that hired a defensive-minded coach since 1999 and, according to FO, saw immediate and dramatic improvement on that side of the ball: the Jets (Rex Ryan in 2009), Browns (Butch Davis in 2001), Colts (Tony Dungy in 2002), Panthers (John Fox in 2002) and the Broncos (John Fox in 2011).