Today’s guest post/contest comes from Thomas McDermott, a licensed land surveyor in the State of California, a music theory instructor at Loyola Marymount University, and an NFL history enthusiast. As always, we thank him for his hard work. You can view all of his work at Football Perspective here.

---

If you can get five people in a room to agree on what a sports dynasty is, you’ll probably have achieved the most miraculous agreement in history since the Congress of Vienna. We know a sports dynasty when we see one (the current Patriots, the New York Yankees, 1990s Bulls, etc.), but it becomes less clear once we attempt to actually define it:,When does the dynasty start? How long must it last? What are the requirements?

In this article on NFL dynasties, FiveThirtyEight does a nice job of negotiating the quagmire by just listing the “best team over any number of years”. ^[1]Their definition of “best” being their ELO ratings. I’m going to do the same thing here, but focusing solely on NFL defenses since the merger (regular season only). The metric is points allowed by the defense (meaning: fumble, interception, kick and punt return touchdowns, and safeties aren’t included), adjusted for era and strength of schedule (basically, SRS ratings). Regular readers may recall that I published these results back in August 2015. To differentiate this stat from Pro-Football-Reference’s DSRS, I’ll call it “DfSRS”.

Below is a table of defensive dynasties, ranging from 1 to 15 years:

I’m sure none of you reading this are surprised by the teams that show up here; all the heavy hitters are there, including the recent Seattle defenses. As noted, dynasties can be hard to define, but we can be sure that being consistent is one of the key ingredients, and the Seahawks defense has certainly been that. Below is a table showing how they’ve ranked in various metrics in the past 5 years:

Pretty impressive, and no doubt, that’s a dynasty. How does their 5-year run compare to the two legendary teams that are ahead of them in that category?

While the Seahawks don’t have those absolutely “elite” regular seasons — the Bears and Steelers both have two years of +8.0, and the Seahawks have none — they have the highest “worst” year out of the three. To underscore how remarkable their run has been, it’s worth taking a look at their contemporaries. Below is the Seahawks’ 5-year run compared to the current 5-year runs of six other teams that have had (or have) good defenses:

Carolina had a fantastic 2013, only to drop to average the following few years; the 49ers were great in the Harbaugh years, dipping in 2014 and then mediocre in 2015; the Bengals, Chiefs and Cardinals have been consistently good but not great, and Denver has two average and below average years sandwiched in between three good/great years. It’s not easy to be consistently great, year after year.

I’ll be watching the Seahawks closely this year. If they can hold teams to around 15 or 16 points per game (no easy task), they’ll replace the Bears as having the best 6-year dynasty, which, to me, is historically significant. Over the last five years, Richard Sherman, Bobby Wagner, and Earl Thomas have been three of the top defensive players in the NFL: Sherman and Thomas are two of just seven defenders with three first-team All-Pro nods since 2012, and Wagner ranks fifth in AV among all defensive players over the last five years.

A few other comments:

• This analysis is doing a big disservice to the Minnesota Vikings by making 1970 the cut-off year. In 1969 the Vikings DSRS was 10.6, and I’m sure if we remove “non-defense allowed” scores that number wouldn’t change much. Including that 1969 season in the survey puts Minnesota at the top of the “Elite” ranking, and would easily give them the best three and four year runs. For future posts, I’ll take a stab at incorporating pre-merger years.

• You might be surprised to see the Ravens showing up to the party so late – they don’t break into the table until we hit the 13-year run. There’s no doubt they are a defensive dynasty, but they had a lot of ups and downs, with great years interspersed with some down years. For example, their 5-year run surrounding their Super Bowl win in 2000 looks like this:

As noted, it’s hard to be continually be great, year after year, for any length of time.

• The 1970s Dolphins are another team that shows up late; as good as they were, they just weren’t as dominant as the other dynasties. If I included the 4th and 5th best dynasties, they’d most likely start showing up in the 4-6 year ranges.

• Other dynasties that aren’t listed but would appear if I showed more than just the Top 3:
  • Jacksonville Jaguars, 2004-2007
  • Los Angeles Rams, 1973-1978
  • New Orleans Saints, 1986-1992
  • New England Patriots, 2003-2010
  • New York Giants, 1981-1990
  • Pittsburgh Steelers, 1990-1996
  • San Francisco 49ers, 1981-1992

• I didn’t run the numbers, but my hunch is that if we keep stretching the length of the dynasty out, the Pittsburgh Steelers would probably continually be at the top once we pass 25 years or so. They really have three distinct defensive dynasties, and when these connect, I don’t see any team topping them:
  • The Steel Curtain years, 1972-1979
  • The Greg Lloyd/Kevin Greene/Rod Woodson years, 1990-1996
  • The Troy Polamalu/Dick LeBeau years, 2004-2012

• If you’re thinking playoff success should be considered when ranking dynasties, you’re 100% correct. I’m working on a way of including that; maybe some kind of point system or perhaps just add in points allowed above expectation for each playoff game, etc. Definitely worth doing for something like this.

Thanks for reading, would love to hear your thoughts.