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Was the Seahawks' Legion of Boom actually worse in 2015?

Now that the Seahawks have Brandon Browner back, what became of Seattle's pass defense in his absence?

By Lars Russell
Scott Olmos-USA TODAY Sports

DK note: Everyone please welcome another contributor to the Field Gulls fold, Lars Russell. Here's his first column!

On November 29, 2015, the Seattle Seahawks beat the Pittsburgh Steelers 39-30, coming from behind at home.

The victory gave lots for fans to celebrate. Russell Wilson famously won for the first time in his career when the Seattle defense allowed more than 24 points. Wilson also overcame flu symptoms to throw five touchdowns with no interceptions. Oh, and it was his birthday. Doug Baldwin scored three times, including the dramatic 80-yard game-clincher on 3rd and long. Thomas Rawls added 81 yards and another touchdown to his own brightening legend.

Beyond that, if it didn’t exactly put away the crock pot from Super Bowl XL, the win at least exacted some relief for the ignominy over the years from seeing Seattle get shut out in both chances in Pittsburgh to place a lid over that simmering beef. More important for the 12-week-old season, the game notched the Seahawks’ first win in five tries against 2015 playoff contenders.

But it wasn’t all great. Steven Hauschka got an extra point blocked and the Seahawks failed on two other two-point tries. Jimmy Graham suffered his season-ending patellar tendon injury trying to make a catch in the end zone. That part sucked.

Oh. And Seattle’s vaunted defensive backfield, the Legion of Boom, surrendered 37 completions for 480 yards. That too was sucky.

Not 480 all-purpose yards. Not 480 yards total offense. 480 yards passing. That was the talking point. This arithmetical detail, bunched with highlights of Markus Wheaton running free in the deep middle, made some of the league’s most astute, most analytically-minded observers ready to say the Seahawks were missing the defensive dominance that had propelled them to consecutive Super Bowls and a world title.

"The defense is just not great anymore," deemed Yahoo’s Frank Schwab. "The Seahawks’ winning formula has changed beyond recognition," Mike Sando declared. (Sando emphasized the offense’s breakthrough, true, but also indicated how defensive vulnerabilities demanded it.) Meanwhile, former Football Outsiders guru Mike Tanier singled out Cary Williams, DeShawn Shead and Jeremy Lane, "Three great defensive backs and three terrible ones may not be much better than six half-decent guys." Ouch.

Pointing out Williams was in fact inactive for that Steelers game—that it was the first activity for Lane at all, after rehabilitating his injuries from the Super Bowl—doesn’t discount Tanier’s critique. These revolving circumstances at cornerback, plus troubles with depth and dissension at safety, were considered the reasons Seattle’s defense had struggled against winning teams. The reasons why five opponents had passed their way to comebacks following Seahawks 4th-quarter leads.

Indeed, at 6-5 beating Pittsburgh made it the first time all year the two-time defending NFC champions’ own record went over .500.

So even though this time it was Seattle avoiding the catastrophe, that jagged number hung on the back end—480 yards!—supported a new consensus wanting to seal the era of Seahawks defensive supremacy now firmly in the past.

A week later the Seahawks cut Williams, so clearly they saw a problem too. But was it already too late? Changed beyond recognition. How bad was the Seahawks defense? Six half-decent guys. Had the mighty Legion of Boom shriveled into some sorry Legion of Doomed?

Naturally not everyone agreed.

Schatz was right, of course. Ben Roethlisberger, who had missed all of October with a sprained MCL, in November started throwing balls like an 18th-century Russian heiress. The Steelers quarterback and his pass catchers spent six weeks averaging 348 yards per game even if you don’t count the extreme output in Seattle right in the middle of it. One week earlier, Roethlisberger torched the Browns for 379 yards and three touchdowns. The next week he tossed up 364 yards with four TDs against the Colts. With his advanced posse running routes, defending the Steelers probably felt like working an Etch-a-Sketch with three knobs.

But Schatz was also understating what happened. I mean, 480 passing yards doesn’t just sound like a lot of yards. It is bad. Only 20 times in all the games played in all the NFL seasons since the 1970 merger have teams given up more raw passing yards in a single game. And five of those took overtime to get them there.

(To understand how rare this is, the Steelers as an organization have played 712 regular season games in that time—and they’re only one team. We’re talking 20 times in 10,000-15,000 games league-wide.)

Besides the critics were gauging the Seahawks not against Pittsburgh’s offense or the worst defensive outings ever recorded, but against their own historically great squads of the past few years.

Top football defenses may be expected to be fast and perhaps are inclined to be furious, but they’re not supposed to measure themselves a quarter mile at a time. (480 yards = 0.27 miles.) In 2013, Seattle gave up even half of 480 passing yards just once in the regular season (325 in the OT classic in Houston in week 4), while the 2015 Seahawks had now already allowed at least 240 through the air six times in 11 games.

Seven times if you count that Pittsburgh did it twice in this game!

So in a way those condemning comparisons were fair.

But—also totally unfair! Because the 2013 Seahawks gave a performance so outlying that it might not be possible yet to put any recent season in proportion.

What do I mean? Let’s look away from yards per game, because NFL teams pass so much more often and so much more effectively than they used to that passing totals make it hard to compare success across time. For instance, half of those 20 480-yard passing days over 45 years have come in the last 10 years. And Seattle’s Super Bowl-winning unit doesn’t come anywhere near the top of a yards/game list historically.

Yet the Seahawks that year allowed just 3.2 adjusted net yards per pass attempt.

ANY/A avoids the volume issue by measuring passing as a rate, and is handier for examining defense than plain Y/A because it factors in sacks and interceptions to count pass defense’s influence on plays that don’t end in completions.

To correct for the season’s attitude toward passing, Football Perspective’s Chase Stuart subtracted ANY/A from the NFL average (6.0 in 2013, putting the Seahawks defense 2.8 yards per pass attempt better than average) and then used the distributions in these data to find that this differential is better relative to its year than every team’s since 1988 except the 2002 Tampa Bay Buccaneers’. Check it out: They’re third best after 1970, and fourth best ever (or at least since 1950 when Stuart’s stats begin measuring this).

So the Super Bowl Seahawks were great. We can always high five about that. But using ANY/A we can also see how the degree they stand out from the norm highlights how much variance defenses tend to exhibit in this regard. Look at the top chart here, in which Stuart shows each team’s differential ANY/A allowed relative to league average in each year prior to 2015 since the NFL expanded to its current 32-team configuration.

Only the rarest pass defenses sustained success relative to the rest of the league for more than two or three years at a time, while even those streaks of dominance contain a lot of haphazard fluctuation within the trend. For example, the only team that posted a differential at least 2.0 ANY/A better than league average that also held within a whole yard of that per-play advantage in an adjacent year was the 2005-06 Chicago Bears (a 0.5-yard decline)—and one year removed from that stretch in either direction were basically back to league average. Few enough defenses (less than 2 percent) ever posted rates better than 2.0 yards better than average at all. Indeed Seattle from 2012-2014 is comfortably the only team since 2002 to post three straight years better than even 1.0 yard better than league average (and they almost did it in what would have been the first of four times in 2011, with a per-attempt differential of 0.9 yards).

Defensive performances are in the NFL nearly impossible to maintain season-to-season at the extremes.

Part of this is no doubt due to player and coach movement, aging, injury and all the elements that might otherwise describe a Seahawks decline in 2015. But none of that explains why offensive consistency is more predictable from year to year. Defensive success can be contingent on turnover luck, sure. But I think it’s also just the adaptive, almost complementary nature of defense—which regardless of success (or specifically owing to it) never totally dictates the offensive inputs or styles, or game states, it encounters. Offenses get to be more reliably themselves.

So when deciding whether or not current Seahawks defenders meet standards set by their former selves/units, it’s helpful to remember this inherent defensive relativity. Even good pass defenses necessarily demonstrate considerable variance year to year, and Seattle in 2013 was an outlier even within a context of continued excellence unprecedented for its era.

The 2014 Seahawks allowed 5.0 ANY/A for the season. Noticeably, that’s more than a yard and a half worse than the mark the year prior, even relative to an NFL which also got a little worse (or QBs were better, whatever). But with a differential 1.1 yard per attempt better than average, it was still third best in the league. And did anyone then argue they went to the Super Bowl lacking a feared defense carrying a heritage among the greatest of all time?

But since we now have this other tool for analyzing pass defense, let’s go back to that Steelers game. Roethlisberger and friends passed for 480 yards, as everybody remembers, but how did Pittsburgh do on a per-play basis? How bad was the Seahawks defense that day? Oh. Turns out ANY/A allowed was 5.2.

Oh.

Ohhhh.

Now, it’s true this particular figure is more useful for showing performance across a larger sample than one game. ANY/A is a stat particularly sensitive to interceptions and in this case Seattle picked off Pittsburgh four times, including two from backup Landry Jones. But the other detail deflating the Steelers’ ANY/A is their high volume of pass attempts deposited a pretty large sample. If Pittsburgh put up two games worth of yards on the Seahawks it’s also true that the Legion of Boom absorbed almost two games worth of passes (59).

I would say the Steelers abandoned the run but they never even made eye contact with it. Roethlisberger threw 20 passes in the first quarter and Pittsburgh called only nine runs all day not counting quarterback sneaks and scrambles, even though it led most of the game.

Executing this peculiar strategy, Wheaton memorably got behind a few coverages but Martavis Bryant and Antonio Brown were mostly bottled up. Even excluding Jones’s four attempts, Seattle held peak Roethlisberger (11.6 ANY/A during his crazy streak) to a not-historically-out-of-control 6.6 adjusted net yards per attempt.

But let’s make this an even larger sample. How much worse was the Seahawks’ pass defense overall in 2015? We now know discarding Williams and integrating Lane helped restore some security in the secondary, but that change couldn’t undo the damage taken during the first three months of the year, right? It certainly didn’t change the prevailing narrative that Seattle’s pass defense took a step back last season—and then hesitated as a receiver blew past it in the seam.

Yet if you look at the season as a whole the Seahawks allowed 5.2 ANY/A for the year, deviating from the previous year’s figure by just 0.2 yards per play in a highly volatile statistic. Oh. By comparison, among the other top-five pass defenses from 2014, the Bills (4.5), Browns (5.0) and Lions (5.1) all turned significantly for the worse (6.1, 7.8 and 6.9 ANY/A respectively). The Broncos (4.9) of course got slightly better (4.7). Meanwhile the NFL average crept up again, to 6.3, meaning Seattle’s relative ANY/A differential was again 1.1—identical to 2014 and now officially more than a yard better than league average for the fourth straight year.

Oh.

Adjusted net yards per pass attempt isn’t the only way to measure sound defense (for what it’s worth Seattle’s pass defense DVOA in 2015 was third in the league at -9.8%, virtually the same as 2014 when it was -10.3% and also ranked third). But it does give a more advanced way to see how the Legion of Boom executed when its opponent tried a radically imbalanced plan. And it shows the 2015 Seahawks remained at the top of the league in a category where no other recent teams have been able to stand their ground so long.

Sounds to me more like continued excellence carrying a heritage among the best all-time than six half decent guys who just aren’t great anymore.

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