Defensive Efficiency Scores: Adjusted Points Per Game
This is the first part of a series on Defensive Efficiency Scores. You can find my discussion of Offensive Efficiency Scores (O-SCORE) by clicking here.
How do we measure defensive success? On offense, I measured success by:
Points Per Drive
Yards Per Point
Yards Per Drive
On defense, it’s going to be a pretty similar scoring system – although I expect the weighting of the variables will be slightly different. The first thing to consider is what I call Adjusted Points Per Game Allowed. This is measured by:
[Defensive Points Allowed – Defensive Points Scored]/(Games Played)
Here are the best and worst AdjPPG defenses since 1970:
One thing which will surprise a lot of people is that the 2000 Titans score better with AdjPPG than the historic 2000 Ravens. How is that possible? The Ravens allowed 153 points to Tennessee’s 173, but Tennessee’s defense scored 5 TD’s (30 points) to the Ravens’ 1 TD (6 points). So put another way, the Ravens did more to stop their opponents from scoring, but the Titans’ D did more to positively affect the scoreboard. That said, I’m not sure of too many people – if anyone – who would put the 2000 Titans’ defense ahead of the Ravens that year.
Looking at these numbers, there’s something else which stands out – there are a lot of teams from the 1970’s in the first list and not too many in the second list. While average PPG hasn’t changed all that much over the years (about 2.5 points), it’s enough to make a pretty big difference in this list. A better way to look at it is by taking AdjPPG+, calculated as:
This gives us the ratio of a team’s AdjPPG relative to league average:
Still a lot of teams from the 1970’s, although we see the best teams from the early 2000’s jump up the list a little. Interestingly, there isn’t a single team from the 1990’s on the top 20 list (The 1999 Rams and 1990 Giants are the best of the 90’s in 29th and 30th place, respectively). The 1970 Vikings allowed 63% fewer points than league average, a truly impressive feat which will be almost impossible for anyone to top.
Here’s the worst:
The 1981 Colts are almost in their own class of ineptitude. They allowed 72% more points than the average team. The 1972 Patriots (67%) are a somewhat close 2nd worst but after that you don’t have anyone greater than 60%.
As with the offense, total PPG don’t tell the whole story. The next part of this discussion will look at Defensive Points allowed Per Drive (DPPD).