By Kurt Bullard
A few days ago, I wrote this post about whether or not to consider the strength of an opposing defense in choosing what running backs to start in your fantasy lineup. Today, I’ll do the same for quarterbacks.
Personally, I’ve always adopted a strategy during drafts where I take two borderline top 10 quarterbacks with the intention of alternating my starter based on matchups. But is there a chance that the strength of opposing defenses doesn’t even matter and that one might as well leave it up to chance?
I looked at quarterbacks from 2011-2014 in games where they completed more than four passes. For each game, I examined how they played compared to their season average by calculating the difference between that week’s points and their per-game average during the year. I then regressed these residual week totals against the defensive DVOA of the team as well as whether a quarterback was on the road or at home and what week of the season it was.
The regression returned the following results:
As is shown here, the defensive DVOA is a significant variable in predicting how a quarterback performs on a week-to-week basis if you know, on average, how good of a performer is. Whether a team was on the road and the week of the season was also significant in predicting deviation from the average performance of a QB, although the latter was minuscule.
But yet again, like running back performance, the level of defense explains very little. The effect of the defensive strength of an opponent is actually not that large on average. The expected points gained from starting a running back going against the league’s worst defense last year instead of a league-average D would have been 2.72 points on average (16.73*.163). That’s not a huge jump and not a reason to panic over who to start one week.
Perhaps more importantly, the defensive strength of a team only explains 4.6% of the variation in the data. In other words, on an individual week-by-week basis, knowing the opponent’s DVOA on defense would tell you very little about how the running back actually did that week. Whether it be other factors – weather, specific scheming that week, or just general randomness in performance, defensive strength tends to get clouded out.
So if you really need a tiebreaker because two quarterbacks have been performing equally well, looking at the defensive strength of a team can help. But anything more than that, and you’ll find yourself stressing out for little reason.