Chicago’s defense was really, really good in 2018. They led the NFL in points allowed, turnovers forced, touchdowns scored, and passer rating against, and finished 3rd in both yards and sacks. They finished as the runaway best defense in Football Outsiders’ DVOA, which is intended to be an all-encompassing metric, and even finished as the 8th best defense ever in DVOA’s database, which runs back to 1986.
Now as we head into 2019, fans are rightly wondering if Chicago’s defense can repeat that performance. While I won’t pretend to be able to predict the future, I can look at the past to see what it might have to tell us. So I looked at top defenses in recent NFL history and measured, through a variety of metrics, where the 2018 Bears excelled. Then I looked to see how they followed that up in the next season. Full data collected can be viewed here for transparency’s sake.
The DVOA system is set up such that an average defense gets a score of 0, with negative numbers indicating you are better than average (the farther from 0 the better). The Bears finished with a final score of -26.0, so I looked at other teams in the last decade (2008-17) who finished at -20 or better. This was quite a small list, as it featured only 10 teams. Here’s how they fared in the season following that dominant performance:
- Average DVOA: -25.1%
- Average following DVOA: -8.8% (8th in NFL)
- Change: 16.4%
- # teams with better DVOA following year: 0
- # teams top 5 in DVOA following year: 5
- # teams top 10 in DVOA following year: 8
- # teams below average in DVOA following year: 1
First, notice that none of these defenses were as good the following year. This isn’t surprising; there were only 10 teams in 10 years who achieved this caliber of DVOA. The odds of doing that twice in a row are very low.