Fantasy Football: Is the Seattle Seahawks' Defense Worth Drafting Anymore?

Imagine: it’s the year 2013, and you are an NFL offensive coordinator. Even worse, pretend you’re an NFL offensive coordinator facing the Seattle Seahawks defense just as their soon-to-be iconic “Legion of Boom” secondary is hitting its peak.

Featuring the stylings of physical cornerbacks Richard Sherman, Brandon Browner, and Byron Maxwell, as well as the rumbling hits of safeties Earl Thomas and Kam Chancellor, this defensive unit became one of the most feared in the league during the early part of the decade.

It also prompted fantasy players to rabidly draft the Seattle Defense/Special Teams unit at the 88th pick of fantasy drafts, or the 4th pick in the 8th round of 12-team leagues in 2014 (per FantasyFootballCalculator). Yikes.

While that is obviously much higher than we at numberFire prefer you draft your fantasy defense, the Seattle defense was a top-notch defense. But their fantasy outlook has gotten even bleaker with the release of Sherman, the retirement of Chancellor, and the impending trade of Thomas.

Now that the Legion of Boom is no more, should your trust in Seattle’s D/ST evaporate with it?

We Are Legion

If you’ve been reading our site for a while, you’ll notice that we’ve done studies on the effectiveness of the Seahawks’ defense with and without Earl Thomas and Richard Sherman, both three-time All-Pros at their positions. Those studies we did using numberFire’s Net Expected Points (NEP) metric, which describes the contribution a play (or player) makes to their team’s chances of scoring. By adding down-and-distance value to the box score production, we can see just how much each play and team as a whole influence the outcome of games. For more info on NEP, check out our glossary.

Defensive NEP is a really good way to analyze an NFL defense’s effectiveness, but it can also be indicative of potential D/ST fantasy scoring.

When we create an R correlation of schedule-adjusted Defensive NEP per play (where more negative values means more points kept off the board) and Team D/ST fantasy points over the last five years, we get a value of -0.66, meaning that there is a strong relationship between the two pieces of data. The more expected points a defense keeps off the field, the better their fantasy scoring will be. This makes sense, considering standard Team D/ST fantasy scoring incorporates the yards and points that unit allows.

So, how do we find a quality defense?

While there’s no guarantee that a good defense one year will continue to be good the next, there is some continuity that bleeds over from year-to-year. By running a correlation calculation on schedule-adjusted Defensive NEP per play from one year to the next, we find a 0.43 R-value -- a weak-to-moderate relationship, but that coefficient plummets to 0.21 when we look at fantasy points.

Basically, it breaks down like this: if you had a good defense on the field last year, it’s likely that they were good on the fantasy gridiron, too. There’s also a reasonable chance they’ll carry over their on-field goodness this year. But, there’s no guarantee that they'll be a good fantasy defense this year.

That may sound confusing, but it's key.

Boom Goes the Dynamite

That’s where we arrive at the issue of the Seahawks D/ST.

Last year, fantasy owners were selecting this unit in the middle of the 10th round, as the 4th defensive unit off the board in redraft leagues. Players like Adam Thielen, Cooper Kupp, Sterling Shepard, Robby Anderson, and many others were going multiple picks (or even multiple rounds) later than this unit. This year, though, the Seattle D/ST is going undrafted. Is this the correct response to their offseason changes?

Based on what our models say, the Seahawks’ defensive unit will likely go from a top-tier team to the ninth-best group for fantasy purposes this year, and that doesn’t seem like a ridiculous notion.

Remember, in an earlier articles, we found that Sherman's presence on one side of the field reduced the value of passes on average by 0.06 NEP per play, and without Thomas, the Seattle secondary allowed 0.08 NEP per play more on drop backs. While this is merely a rough estimate, let’s assume that the loss of both of them -- in addition to pass-rusher Cliff Avril and Chancellor -- reduces their per-play value by 0.10, from 0.01 schedule-adjusted Defensive NEP per play to 0.11 (remember, negative is better for defense).

By comparing that to the average fantasy point total that a defense generating 0.11 Defensive NEP per play earns, we get a projection of 139.26 fantasy points -- just a hair above numberFire’s own projections. In a 10- or 12-team league, we can expect the Seahawks’ defense to still be worthwhile to draft, but they are no longer a weekly lock in your lineups.

Considering their Week 1 and 2 matchups against the Denver Broncos and Chicago Bears, an average undrafted position could make the Seahawks a value as either a last-round target or a quick waiver add (depending on the setup of your league) in 2018.

After that, though, feel free to treat the once ironclad Legion of Boom the way you would any other D/ST: stream, stream, stream.