Where the Seahawks 2013 Defense ranks all-time

          I know some of you reading aren't excited about the all-time ranks because it is impossible to know exactly who is the best.  But, I can't help it.  I love thinking about the all-time greats and with the Seahawks impressive run to a Lombardi Trophy I've been kicking around the topic of where the 2013 Seahawks D ranks compared to the other greats.  Immediately after the Superbowl ESPN.com polled Americans to see where the 2013 Seahawks ranked compared to the 1985 Bears and 2000 Ravens (those were the only 3 on the list).  I voted for Seattle considering what they had just done to Denver's high powered offense and found out that most of America did as well.  So ever since the topic has been on my mind.
          Let me say this too.  For you Seahawks fans I'm not trying to undermine what their team or defense has done.  In fact it's the opposite.  For them to be considered among the greats all-time is a testament to their current dominance.  I'm simply curious where their dominant year ranks up against the best all time.  And keep this in mind too.  I'm not simply exploring Superbowl performances.  So while Seattle's drubbing of Denver may be the best Superbowl performance of all time (debatable), this list is considering the entire season.  Also, I'm not considering a dynasty or set of years.  After all, I can definitely see Seattle winning more Superbowls with this defensive group but that's yet to be seen.  And while the Steelers defenses of the '70s were amazing I'm only considering each on a year to year basis.
          At the outset of my research I was only exploring Superbowl winning teams.  I went back and forth on whether the best defense had to be on the best team.  I discussed the topic with a few and started exploring the greatest defenses all-time regardless of winning the Superbowl.  After I did it was obvious I would have to consider some defenses despite their team not hoisting the Lombardi.  So in a nutshell any team can make the list.
          Another criteria was deciding what year I would start researching.  At first I was going through all the Superbowl years (1966 and on...).  But, before 1970 the NFL and AFL were two separate leagues.  Therefore the 1969 Chiefs, who had an awesome defense, only played the other nine AFL teams during the regular season and playoffs before the Superbowl.  Not too much competition is the big problem there.  But, I am disappointed I can't include the '69 Chiefs, '66 Packers, and '69 Vikings on my list because they all were awesome before the merger.  In fact the '69 Vikings were absolutely nasty.
          While I've chosen numerous statistics to base my judgement of the greatest single season defenses of all-time it should be noted that there are a number of variables I can't take into account.  For instance, defensive scoring average is one of the stats I'm using but if the defense takes over on its own ten yard line than giving up at least a field goal is expected.  Also, any points that the opposition scores, even if it wasn't against the defense, is considered in their "defensive" scoring average.  So the Seahawks may have given up a "pick 6" this year and that goes against their scoring average.  Another variable to consider is how penalties have changed the game.  In 1978, for the first time, defensive backs could only bump the receivers for the first five yards (Mel Blount rule).  In the last 20 years besides pass interference another penalty was added called "illegal contact."  And how can we ignore the fact that within the last 20 years QBs do not take near the hits they use to.  Finally, before 1978, the regular season was only 14 games instead of 16.  For most stats I can manipulate the data to at least limit the discrepancy of this last variable.  But, see what I mean about variables??  However, I will not be deterred!
          Here is a breakdown of the statistics I did use:
- scoring average against (discrepancies pointed out above)
- touchdowns against (I used this to counteract the previous issues...veteran move)
- yards allowed (this one has some hidden variables too because the NFL average has increased over time)
- yards per play (maybe too similar to the previous but I used it)
- turnovers (defenses today collect fewer than those 30-40 years ago)
- touchdowns (how many times the defense actually put it in the end zone)
- shutouts (the opponent didn't score at all)
- all-pro defensive players (all-pro team is the best of the NFL at season's end)
- league leader in core statistics (bonuses awarded to teams leading NFL in above stats)
           Now for the stats above highlighted in orange I broke those up into two separate spreadsheets.  One was for per game averages throughout the regular season.  So for example the 2013 Seahawks gave up 231 points averaging out to 14.4 ppg.  What I quickly found was that the best per game averages were from the 1970s.  Defense dominated the game then.  On average the defenses of the '70s gave up fewer points and yards while also creating more turnovers than any other era.  But as I'm sure you're thinking the game was different then mainly because of rules (penalties...or the lack thereof.)  But, I couldn't completely ignore these stats because some of the numbers are very impressive!  Plus, there were a few teams to elevate themselves out of their era and rise amongst the '70s teams.  That should be noted.
           But, I also developed another way to see how dominant defenses were over the years with the core statistics.  For each stat and team I figured out the difference between the teams total and the league average that particular year.  For example, the Seahawks had 39 turnovers this season.  The league average was 25.4.  So the Seahawks TO difference to the league average was a positive 13.6.  The more I used this idea the more I liked it.  It definitely expels the discrepancies of the average per game because now teams are compared only to their peers of that season.  The one thing I noticed though that caused minor concern was the 1970's defenses had less difference to their peers than other eras.  I think the reason for this is that today there is a bigger difference between the best and worst defenses and the numbers show that.  Whereas in the 1970s there were a lot of teams with good defenses, at least statistically.  It's probably kind of like offenses are today.  Some teams appear real good offensively (Lions) but are they really?  The bottom line here is comparing teams to their peers was a fantastic idea so the results were weighted heavier than the per game results. 
           Finally, I also took into account postseason statistics.  The aforementioned stats were all regular season.  Unfortunately, I only did per game postseason stats so again there are some variables to consider because how the game has changed.  But for that reason and a couple others I did not weigh postseason stats as much as the previous comparison to their peers in the regular season. The stats I used for the postseason were:
- first downs allowed
- total yards allowed
- turnovers forced
- touchdowns allowed
- scoring against
- defensive touchdowns
- sacks
          There was an additional postseason statistic I used as well.  I took a look at each opponent that the eligible team faced.  I took the opponent's scoring average during the regular season and then found the difference in what the eligible dominant defense allowed.  For example the Seahawks held Denver to 8 points compared to their 37.9 scoring average in the regular season.  I did that for each team for each postseason game they played and then averaged out the differences to one number since not all teams played an equal amount of games.  Also, in this stat only, I did not consider points given up in ways outside of the defense.  For example the 2000 Ravens defense did not allow any points versus the Giants in the Superbowl but a kickoff return gave the Giants 7 points.  Those 7 points were not used against the Ravens D.
          Here are a few graphs I thought you might like to see that demonstrate how much the league has changed over the years.  Again, because of these numbers, per game averages aren't solely an effective way in analyzing the greatest defenses of all-time.  That's why I went with the league average comparisons and weighted them more heavily.









            Now this is a lot of info to digest so rather than reveal my rankings now I think I'll create a part 2 page and leave some suspense hanging.  But, to not leave you completely high and dry I'll reveal my top 20 teams in chronological order (Superbowl winning teams are highlighted):

1970 Vikings
1971 Colts
1972 Dolphins
1973 Dolphins
1974 Steelers
1975 Steelers
1975 Rams
1976 Steelers
1977 Falcons
1985 Bears
1986 Bears
1988 Vikings
1991 Eagles
1996 Packers
2000 Ravens
2000 Titans
2002 Buccaneers
2008 Steelers
2009 Jets
2013 Seahawks

            I did want to share a couple amazing statistics I found about teams not on this list as I researched.  1) The 1999 Rams D scored 8 TDs in the regular season.  2) The 1977 Cowboys D created 19 turnovers in three playoff games en route to the Lombardi.  That stat alone had them on the cusp of my list.  To be continued...

Kieth