The Value of Defense

Did you know that Yahoo’s fantasy football’s default settings include an IR spot?  A year ago, I didn’t.  After my meticulous planning and detailed preparation for the fantasy football draft, I miscounted the number of rounds and left the draft without a defense.

However, this miscue, which says a lot about my basic counting skills, is not a death blow to my fantasy season (as long as one is in the lineup by the start of Week 1).  As I’ve written before, certain positions carry less value than other positions based on the difference in fantasy points scored between a player and a replacement player.  Other than kickers, defenses offer the least impact to a fantasy football lineup.  Even the best defenses offer little marginal value, which is why they are usually not drafted early or the subject of a bidding war (if doing an auction draft).  The table below shows the value over replacement player for the top 12 defenses from 2012 to 2016.

From 2012 to 2016, the top defense averaged 66.6 more points than the 13th best defense (in terms of fantasy points scored) from 2012 to 2016, or 4.2 more points per game.  This number drops as we go down the list, where the eighth best defense less than a point more per game than the 13th highest scoring defense.

In my first two drafts this year, I’ve seen the Denver defense drafted at the end of the seventh round in both of leagues.  If I could promise you that the Denver defense will score the most fantasy points of any defense this year, then this pick actually makes sense.  But I find it unlikely that we can project the top defense before the season starts (it’s more likely to be Seattle) given that the success of a defense is partially dependent on the offenses that the team faces.  This is why I will usually stream a defense for the best matchup.

Truly, however, the success of a defense in fantasy football is mostly dependent on random events such as interceptions, fumble recoveries, and return and defensive touchdowns, which are all highly unpredictable and exhibit significant variation.  Holding the quality of the defense fixed, the worse the offensive team (or, more precisely, the more likely the offense to surrender a turnover), the better the matchup.

Ideally, the overall ability of the offense should not be the main factor in determining the strength of the matchup.  Rather, the likelihood of the opposing offense turning the ball over is a better screen.  As defenses score the vast majority of their points from turnovers and sacks, which are not necessarily a product of the success of the entire defense, like points and yards allowed.  In fact, defenses averaged 0.7 fantasy points per game (of a total of 7.4) over the last five seasons from points and yards allowed.  Additionally, the table below shows the percentage of defensive fantasy points from each way that defenses can score fantasy points (sack, safety, interception, fumble recovery, defensive touchdown, and return touchdown).

Sacks account for nearly 1/3 of all fantasy points over the last five years, followed by interceptions at nearly 1/4.  Of the ways that defenses score points, only sacks are a function of the ability of the defense, or at least the team’s pass rush (other than coverage sacks).  Teams with high sack totals may not score a large amount of fantasy points in a given week, but they can serve as a more reliable source of fantasy points.  And if you drafted Denver in the seventh round, don’t be too mad at yourself.  They’ve generated 228 sacks over the last five years (it’s nice to have Von Miller), one behind the league leading Carolina Panthers.

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