I wrote about it a couple times earlier in 2010, but this chart fully shows how much our 2009 defensive projections sucked. The correlation between our projections and teams’ actual defensive DVOA was pretty much zero — in fact, it was on the negative side of zero. A dartboard would have been just as accurate. When we added up offense, defense, and special teams to get our total DVOA projections, we ended up with the opposite of what actually happened with NFL teams: our poor defensive projections overwhelmed our quality offense and special teams projections, leading to the worst projections we’ve done in six seasons.
There are two explanations for what happened last year (and I refer more to the overall NFL offensive numbers than I do to our projections). The first explanation is that something in 2009 dramatically changed in the way NFL teams build their rosters and turn over their talent from season to season. Because of this change, most NFL offenses in the near future will barely decline or improve from year to year. In addition, old trends that indicated when teams might improve or decline no longer apply, which means that projections based on previous data (such as ours) are now useless.
Or, 2009 was a bit of a fluke year.
Occam’s razor points to the second explanation, and I’m inclined to agree. Of course, that doesn’t mean I wasn’t crazy busy this offseason, trying to rework the projection system and identify whatever caused changes from 2008 to 2009 without changing anything in the system based on the trends that indicated improvement and decline in previous seasons. However, I think it is safe to say that 2010 NFL offenses will not be as similar to 2009 NFL offenses as the 2009 NFL offenses were to 2008 NFL offenses — and the projections in Football Outsiders Almanac 2010 will come closer to matching the accuracy we saw in 2007 and 2008.
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