100 Fantasy Football Tips in 100 Days, Day 27: Projecting Defenses
In my new book Fantasy Football for Smart People: How Fantasy Football Pros Game Plan to Win, I looked at the consistency of defenses from year to year.
I looked at the year-to-year correlation for each team’s pass defense, run defense, and interceptions.
These numbers are pretty shocking. First, we see that there’s been just a tiny correlation in a team’s interception rank since 2010 (an average of just 0.139). On a scale of -1 to 1, that’s good evidence that defensive interceptions are pretty unstable, which was to be expected.
Surprisingly, the same goes for pass defense. The correlation between pass rank in 2010 and 2011 was actually -0.295. A negative correlation indicates that the worst pass defenses from 2010 actually became the best in 2011, and vice versa. That alone suggests that pass defense isn’t predictable (and thus not useful when projecting strength of schedule).
However, take a look at run defense. The average correlation coefficient since 2010 is 0.430 (and 0.529 since 2007), meaning there’s a good chance that good run defenses remain good and bad ones stay bad.
Read more on defenses in How Fantasy Football Pros Game Plan to Win.