(Kirby Lee/USA Today)
Perhaps the most underrated unit in football due to playing alongside their historically good defense, the 2013 Seahawks’ offense scored the eighth-most points in the NFL and were tied for fifth in points per drive. Some attempt to diminish the unit by pointing to their middle-of-the-pack yardage total (17th in the NFL) and drawing attention to the short fields they often work with, but Seattle was an above-average rushing team (4.3 yards-per-attempt) and Russell Wilson finished his second year in the league ranked fourth in passing Y/A and seventh in Adjusted Net Yards per Attempt. The unit racked up points when needed and was consistently efficient, grading out ninth in offensive yards-per-play.
Seattle wasn’t healthy, either. The team welcomes jack-of-all-trades Percy Harvin and Pro Bowl linemen Russell Okung and Max Unger back in to the fold this fall with open arms; the trio missed a combined 26 games between them in 2013. Leading receiver Golden Tate was thanked for his services and told to go take Detroit’s money, but the rest of the Seahawks’ young offense remains intact and has accumulated another year’s worth of seasoning. Although Harvin’s health remains a permanent question mark, rookie receivers Kevin Norwood and Paul Richardson could both replicate the impact of Jermaine Kearse’s first year.
But while Seattle’s offense is locked and loaded for the repeat, most would agree that their defense remains the key to winning another Super Bowl. It boasts virtually the same personnel as last year’s unit that led the NFL in almost every meaningful metric, and their all-time great secondary doesn’t expect to miss a beat with Brandon Browner off in New England and Byron Maxwell tabbed as Richard Sherman’s new Robin.
With only four repeat champions in the last quarter-century, though, the common logic is that a Super Bowl winner will regress when given a new 16-game slate with a target on its back. This isn’t exactly controversial; the first-place finisher among a 32-team field is usually due for some regression to the mean. But comparing Seattle’s 2014 defense to, say, that of the 2010 Saints or the 2000 Rams does very little for me. They were champs the year before, but those defenses weren’t in the Seahawks’ class during their title run and they certainly weren’t expected to be as good as the 2014 Hawks during their repeat.
I want to compare Seattle strictly to other historically-good defenses — defenses that finished a full two standard deviations better than the league average in points allowed. Only 21 defenses have registered on that scale since the 1970 AFL-NFL merger, and they’re listed below chronologically along with their z-score:
And here they are sorted from highest z-score to lowest:
Disclaimer: a higher z-score doesn’t necessarily mean a better defense. Some may wonder why the unheralded ’95 Chiefs rank higher than iconic units like the 2000 Ravens, ’85 Bears, and ’71 Vikings, but standard deviation is just as influenced by those who perform below the mean. 1995 saw the average team allow roughly 344 points over the course of the season, almost 20 more than those in ’94 (324.1) or ’96 (326.8) and well over what teams were ceding two years prior (299.2); I have a sneaking suspicion that the addition of Carolina and Jacksonville as expansion franchises diluted the available talent pool that season, creating a crowded cellar. 1995 was home to the lowest standard deviation (39.2) of all the years I calculated them for — most registered in the 50s and 60s. So while Kansas City’s points allowed total of 241 was a mere 102.8 below the mean, that tiny standard deviation resulted in the third-highest z-score since the merger. The 1975 Rams, on the other hand, allowed 153.3 below their mean but were saddled with a league-wide standard deviation of 68.4.
So we know that these defenses were elite in that calendar year, but how did their successors fare? How many stayed that dominant, how many were merely great, and how many saw precipitous declines?
As illustrated with my primitive Excel skills, here is a visual representation of how those defenses fared in successive seasons. N represents the original year listed in the first graph, and n+1 is the following year.
The top-rated defense by this measure, the 2006 Baltimore Ravens — they of the six Pro Bowlers and 12.6 PPG allowed — saw the largest variance in performance, regressing into a team that fell almost a standard deviation below the 2007 mean. The ’95 Browns and ’89 Bears also sported below-average defenses, but overall this sample fared better than I expected it to. Of the 19 defenses we can extrapolate from, 16 remained above average, nine were a full standard deviation above the mean, and four posted another two-standard deviation season (including the 2012-2013 Seahawks).
However, only two improved compared to the league average — 2013 Seattle and 2011 Pittsburgh. And while the Buddy Ryan-built Bears posted three such seasons in four years, no franchise has been that much better than the mean for three consecutive years like the Seahawks are vying to be.
But Seattle doesn’t need to be this good to win another Super Bowl, especially if their offense stays healthy. In layman’s terms, Pete Carroll’s bunch don’t need to be a top-20 defense of all time to take home another Lombardi. It ended up last season that the division rival 49ers were their only peer, after all; Peyton Manning still doesn’t know what hit him back on February 2. This franchise has already defied statistical probability by improving upon a historic season once, though, and unlike many of their fellow members of the two-standard-deviation club, Seattle returns almost the entirety of their defense and are one of the youngest teams in the league.
The Seahawks are technically gunning for a repeat next season, but they’re also in pursuit of the first z-score three-peat. It should be a blast to watch unfold.