The Fantasy Mythbusters: Are Bye Weeks, Short Weeks & Jet Lag Significant?
Football is among the most physically demanding of sports; this is primarily the reason that there are so few games. The NBA plays over 70 regular-season games a year and the MLB over 150, yet NFL franchises suit up for just 17 weeks (16 up until this year). In addition to this reduced schedule, teams have one ‘Bye Week’ a year – a week where they don’t have to play – baked into the schedule. On the flip side, teams will sometimes play on Thursday Night Football and thus have a short week: just 3 days in between the game Sunday and Thursday to rest and recuperate.
Conventional football wisdom states that teams have an advantage coming off of the Bye Week: they are better rested, have had the chance to practice more, and have had more time to develop a game plan. The exact opposite theory generally holds for teams coming off of a short week: in general, Thursday Night Football has a reputation for being pretty sloppy for exactly that reason.
Does this have any implications for fantasy? The 2021 season is well underway and, while I hope that your team is undefeated, it’s likely that even the best-laid plans have gone awry; the mounting toll of injuries alone can disrupt even the most formidable roster. In this vein, it’s important to try anything and everything to get an edge over your opponent when making roster moves and start/sit decisions. This article will examine if there is indeed a performance boost for players coming off a bye (and the reverse for those on a short week).
We’ll be looking at data from 2010-2020 from nflfastr. The data collection process is simple: we take a collection of crucial offensive statistics (yards and touchdowns for both rushing and passing, as well as interceptions) from all games Week 5 onwards. From here, we mark the games where the offense is coming off of a bye (two weeks in between games) or a short week (5 days or less) and do the same for the defense.
The last step is to control for team skill. For example, if we are looking at passing yards, we take the average passing yards gained (for an offense) and allowed (for a defense) over the past four weeks. This allows us to isolate the effect of bye weeks and short weeks instead of our results being confounded by team skill. It’s likely that over ten years, the results would balance out anyway, but it’s a nice measure to take. We wouldn’t want the TNF passing numbers to be skewed downwards just because these games consistently feature the Jaguars (sorry Jags fans).
Without further ado, let’s get to the charts. Each number here represents percent performance vs. all NFL games; so, for instance, a number less than 100% means that production is lower than average (and vice versa for numbers above 100%). We’ll start with offenses:
This chart looks like we would expect it to look: Rush Yards and Pass TDs are higher for offenses coming off of bye weeks, while Interceptions are lower. Rushing touchdowns and Passing Yards don’t see a huge difference.
Unfortunately, though, most of these differences aren’t large or statistically significant. Offenses coming off a bye throw for .05 more touchdowns on average (fractions of a fantasy point), and even that small number is far from significant. Similarly, offenses coming off a bye throw for .04 less touchdowns on average (less than 0.1 fantasy points), which are also not significant.
The story is a bit more compelling for rushing yards. Teams coming off of a bye do rush for about six more yards on average, and this is very statistically significant. Again, though, this doesn’t represent much of a fantasy impact: that’s 0.6 points per game spread out across multiple players that run the ball on a team.
Let’s see if the story for defenses coming off of bye weeks is more interesting:
The chart is a bit more surprising here: offenses actually pass better (more yards and touchdowns) when defenses are coming off a bye, and rush worse (fewer yards and touchdowns). Defenses, surprisingly, intercept the ball less when coming off of a bye.
Again, though, these differences aren’t very salient. Teams throw for about 0.10 touchdowns more when the opposing defense is coming off of a bye, a number that is decently statistically significant. The biggest difference, again, is rush yards: offenses rush for 8.5 fewer rushing yards when opposing defenses are coming off of a bye, a number that is highly significant.
Short Weeks and Jet Lag
We’re just going to have one chart here because of simple symmetry: when an offense is coming off of a short week, the defense is too, since it’s Thursday Night Football! Therefore, this chart will look basically the same for just offenses and defenses.
These results are all over the place. Passing looks better coming off a full week, while interceptions seem to be way lower on a short week. Still, this difference is just about .10 interceptions and, while it is statistically significant, that’s just 0.2 fantasy points per game. I’ll save you the time: none of the other differences are very large or significant.
Finally, to try to salvage some interesting tidbits out of this, we can look at teams that are jet-lagged. Specifically, that means any team located in the Eastern time zone traveling to play a team in the Pacific time zone or vice versa. Here’s a chart for teams going east to west; for example, the Patriots travel to battle the 49ers.
Again, this chart is all over the place (some statistics look better for jet-lagged teams, some for non-jet lagged teams) and I’ll save you the trouble: none of the differences are very large or significant. Even rushing TDs, which look the most different in this chart, see only a .06 expected increase in rushing touchdowns for jet-lagged teams (.36 fantasy points), a number which isn’t even statistically significant. Unsurprisingly, modern NFL teams are adept at managing a mere 3-hour difference!
Busted. One of the only statistically significant differences for both offenses and defenses coming off of bye weeks was rushing yards. At the maximal point, for an offense coming off of a bye and a defense not coming off of a bye, you can expect about eight more rushing yards per game for the offense. It’s nice to have a 0.8 fantasy point edge, but remember that it’s team-wide, not just for one player; this 0.8 points is likely to split between a couple of running backs and maybe even a mobile quarterback. It’s a nice little bump (emphasis on little) if you have a rusher coming off of a bye, but it shouldn’t move the needle for your start/sit decisions.
Short weeks are even less exciting: interceptions are slightly less common, but the difference is simply not that high. This is likely because of a ‘canceling out’ effect: both the offense and the defense are coming off not a lot of rest! In addition, any stated effects of jet lag are likely overrated.
While these results may seem boring, there is often value in finding nothing. You can put aside any (major) concerns about starting fantasy options coming off of a short week, or players that might be jet-lagged (especially relevant given the London games). Personally, I view this as good news: I always like having at least one player active during the Thursday night game.
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