Tuesday, April 15, 2014

Different Measures Of Greatness

The Battle Of The Best series has spurred a bunch of conversation on and off this site. That is always good to see. Football Outsiders was promoting their own measure of the all-time great NFL defenses on their site today.  The differences between their results and mine thus far illuminate the differences in what each is designed to measure. They have the 2002 Bucs ahead of the 2013 Seahawks, and the 2000 Ravens do not even make the top twenty. Which rankings are better? Neither. And here is why.
The numbers presented on this blog and on sites like Football Outsiders, ProFootballFocus, and Pro-Football-Reference represent our different beliefs about what makes a defense great. I may care more about performance relative to the time in which the defense played. Football Outsiders may put more emphasis on the role a bad offense plays in how a defense performs. It is up to you, as a reader, to decide which more closely matches your value system. Look at the rankings from FO:
Football Outsiders Top 20 Defenses of All-Time
You can see that the 1991 Eagles are far and away the best defense in history by their measure. They are not even among the defenses I plan on measuring. Why? They gave up over 15 ppg, finishing 5th in the league that year, 3rd in their division, and out of the playoffs. To be the greatest defense of all-time, you have to prove it when it matters most. That is my value system. It does not mean the FO rankings are wrong. They simply emphasize different things than I would. A snippet from their article explains their reasoning:

You may be surprised to see the Eagles so far ahead of the pack –- I was too. They are generally in the conversation when people talk about all-time great defenses, but not the clear frontrunner. This is partially an issue of a difficult schedule -– their VOA without opponent adjustments is "only" -38.2% -– but that still leaves them comfortably ahead of the pack. The other major reason is their teammates. While the Eagles had an average special teams unit in 1991, that offense was terrible. Their offensive DVOA of -24.6% is the worst by far of any of the other teams with top defensive DVOAs.
It is critical to account for offensive impact on a team's defense. FO is much more comprehensive than my measure in that area, but I would not make that quite as heavy of a factor as they do. It is part of why they have the 2002 Bucs come in ahead of the 1985 Bears, who had a great offense. I have the Bears comfortably ahead of the Bucs and Seahawks. I think it matters that the Bears offense was great, but I think it matters more how outstanding they were relative to the rest of the defenses that year, and that they led the league in points allowed, yards allowed, and turnovers.

The difference between one offense and another is a tie-breaker for me, even if the disparity is great. It is not a primary determining factor. You may disagree, which is what makes the debate fun. One thing that my rankings, Football Outsiders and Pro-Football-Reference all agree on is that the 2013 Seahawks defense was better than the 2000 Ravens defense. That is particularly ironic considering my article comparing the two defenses has been among the most hotly contested.

People will continue to try and dismiss the rankings on this site as biased and homerish. I would be skeptical coming in here from another fanbase as well. As I said from the jump, the numbers are what they are. That is not debatable. My interpretation and weighting of those numbers certainly is. Three teams down, four or five more to go.

Note: Football Outsiders has clarified that the rankings referenced in this article were compiled by a guest columnist, and may not reflect their official perspective. All the points above about different ratings systems still stand. Different systems emphasize different things. All have a place.  

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