As described in our August 16 post the best way to evaluate a team’s defense is to assign a point value to every play the defense gives up. For example giving up 3 yards on 1st and 10 at midfield has a value of -0.01 points from the standpoint of the offenseive team while gaining 3 yards from midfield on 3rd down and 3 has a value of +0.70 points from the standpoint of the offensive team. Turnovers usually hurt the offense by around 4 points.
For the 2008 season here are the Top 5 defenses (ranked in points given up per 100 plays relative to NFL average defense).
1. Pittsburgh -17 points
2. Baltimore - 15 points
3. Eagles -14 points
4. Vikings -12 points
5. Titans -11 points.
Thus for example, Pittsburgh’s defenses gives up 17 fewer points per 100 plays than an average defensive team.
Unsurprisingly the worst defensive team was the Lions who gave up 16 .1 points more per 100 plays than an average team. Next worse defense was Denver giving up 15.6 points more per 100 plays than an average team.
Our metric for measuring defenses is very simple to understand but much better than yards per game which is the usual NFL metric.
By the way the Vikings had the best rushing defense and the Steelers the best passing defense. The Rams had the worst rushing defense and the Lions the worst pass defense.
By the way our results are adjusted for the strength of the passing and rushing attacks faced by the team’s defense.
In our next post we will look at the NFL’s best and worst quarterbacks.
My book Mathletics (out on August 28) describes our methodology in more detail and also talks about rating NBA and MLB players as well as sports gambling.