FO Mailbag: The Effect of Rest on Game DVOA

Tyler P: In my opinion, football commentators and analysts tend to make a big deal out of the duration of time between a team's games. Teams with a bye or a long off week after a Thursday night game have an advantage, while teams coming off of Monday night games or playing in Thursday night games have a disadvantage. I can certainly see how more or less rest and preparation can affect a team, but I'm curious if you've done any DVOA analysis for teams on long/short breaks. How significant is the advantage/disadvantage and is it relatively consistent across teams and years? If there is a difference, is it more prominent for either defense or offense?

Let's tackle the easiest part first. Since divisional realignment (2002-2011), NFL teams have played 1,331 games on atypical rest (i.e., not seven days), which translates to 4.2 games per team per season. Therefore, looking at team trends amounts to small sample size theater. Also, looking at yearly trends devolves into small sample size theater once we realize that, for instance, there are an average of only 12.2 total games per season played on four (11.2) or five days (1.0) rest.

So, with that in mind, let's eschew the specifics in favor of the more general question: Does the number of days between games have an effect on performance; and, if so, is the effect more prominent on offense or defense?

The analysis required three pieces of information:

• The date of each game over the past 10 years.
• The total, offense, and defense DVOA of each team as of the week prior to the game, starting after Week 4 so as to limit the wild DVOA swings early in the season. (You can find these in our Premium database.)
• The total, offense, and defense DVOA of each team during the post-Week-4 game in question. (You can also find these in our Premium database.)

From there, evaluating the questions at hand simply involved math. I calculated the number of days between games for each team each season (after Week 4), and calculated how much each team's game DVOA fell short of or exceeded their DVOA as of the week prior to the game. If more days between games translates to better-than-typical DVOA, we can conclude that there's a positive rest effect; and vice versa. As you'll see, it's not quite that simple.

Our first table shows the leaguewide trend (Note: positive means improvement in all cases, including defense):

Compared to the baseline of a typical seven-day rest between games, it's pretty clear that the only large effect comes on 13-15 days of rest. And of course, the only way a team can have that many days between games is if they have a bye. So really, this is just a bye effect, and the "AGL Chg" columns, which show the average change in Adjusted Games Lost from one game to the next, suggest that one reason for said effect is that teams get healthier during the bye week.

In terms of offensive and defensive splits, the story is basically the same. Teams coming off a bye play better on both sides of the ball, and getting healthier seems to be -- at least in part -- the mechanism for that improvement.

As with any sport, though, you can't ignore home field advantage. So let's see what happens after splitting the table into home teams and road teams (neutral-site games excluded this time; and again, positive means improvement in all cases):

This one requires a bit of unpacking. In terms of a baseline, we see that, given the typical seven days of rest, home teams play about nine percentage points of DVOA better than usual, whereas away teams undershoot their average performance by about eight percentage points. No surprise there.

Otherwise, though, we see that the rest effect seems to depend on whether a team is at home or on the road. In comparison to baseline, home teams wildly exceed expectations with a bye week's worth of rest, but also do so with the shortest rest possible. In contrast, road teams woefully underperform on short rest and don't benefit nearly as much from the bye week. Furthermore, the difference in post-bye performance exists despite both home teams and away teams enjoying similar improvements in team health.

Regarding team units, the story is once again basically the same. Home teams coming off a bye play better on both sides of the ball, and getting healthier seems to be -- at least in part -- the mechanism for that improvement. That's not the case for away teams.

So, to open up the discussion, here's a question for readers: What the heck happens to away teams on long rest? They get healthier during the bye week, but they underperform similar to baseline. What gives?

UPDATE: Since this was designed to be a short XP, I left the following on the cutting room floor. However, the comments seem to be picking up on it, so I feel obligated to post. Here are the stats translated into the rest advantage ("Adv") for a team over their opponent rather than that team's absolute amount of rest.

The main result still holds. The only way a team can have a six-to-eight-day rest advantage is if they are coming off a bye, but their opponent is not. In such cases, home teams benefit from the largest rest advantage (via an AGL change advantage), whereas away teams don't.

Carry on.