Effects of Weather in Fantasy Football

It seems intuitive to believe that weather plays a huge role in the fantasy performance of different positions in the NFL. When we see a quarterback struggle mightily in a snowstorm, it is easy to jump to the conclusion that weather has a significant impact on the fantasy performance of players. When deciding the players to start for a particular week, weather seems to be a reasonable variable to take into account. Another variable to take into consideration when making such decisions is the opponents the players are facing. Is weather as significant to this decision as opponent defenses? The focus here is on quarterbacks and running backs, though kickers presumably could be strongly affected by weather as teams rarely attempt field goals or even kicks for the extra point in extreme weather conditions.

Data on weather information were gathered from Pro Football Reference, which has weather information available for about 75% of the games from 2006 to 2013. This includes the temperature (°F), the relative humidity (%) and the wind speed (mph) of the game.

To get a sense of the direction and strength of the effect of temperature, relative humidity and wind speed on fantasy scores of QB and RB, the correlation between the weather information and the fantasy score of QB and RB is computed.

	QB Fantasy Points	RB Fantasy Points
Temperature	0.0133	-0.0238
Relative Humidity	-0.0406	-0.0118
Wind Speed	-0.0561	0.00308

	QB Fantasy Points	RB Fantasy Points
Passing/Rushing Yards allowed adjusted	0.148	0.112
Passing/Rushing Touchdowns allowed adjusted	0.158	0.110
Interceptions adjusted	-0.0838

There is very slight correlation between fantasy points and temperature, humidity or wind speed for RBs. The correlation is much stronger for QBs, especially for humidity and wind speed. However, the strength of the relationship can be described as moderate at best. Contrast this with the correlation of fantasy points and measures of opponent defenses for QBs and RBs. Opponent defenses are measured as their seasonal passing/rushing yards allowed, passing/rushing touchdowns allowed and interceptions. These are adjusted to the baseline of league average so that changes in the league over time do not affect the results.

The correlation of fantasy points and measures of opponent defenses is much higher, suggesting that opponent defenses play a larger role in the variance of weekly fantasy points of QBs and RBs than weather.

To visualize the difference between the effects of weather and opponent defenses on weekly fantasy performance, we aggregate the games that are most and least conducive for QB and RB performance in terms of weather conditions and opponent defenses. For QBs, favorable weather conditions include above-average temperature, below-average humidity and below-average wind speed. For RBs, favorable weather conditions include below-average temperature, below-average humidity and above-average wind speed. For QBs, a favorable opponent includes a defense with above-average passing yards allowed, above-average passing touchdowns and below-average interceptions. For RBs, a favorable opponent includes a defense with above-average passing yards allowed, above-average passing touchdowns and below-average interceptions. The average player performances for QBs and RBs in these four conditions are displayed below respectively.

The gap between QB and RB fantasy performances in favorable and unfavorable weather conditions is much smaller than the gap between QB and RB fantasy performances against favorable and unfavorable opponents. This further supports the point shown with the correlations that weather is not as crucial a factor as an opponent’s strength when it comes to impacting weekly fantasy performance of QB and RB.

To strip out the effects of random variation and other factors in play, we performed a fixed effects regression that also controls for the surface and location (home/away) as well as weather conditions and measures of opponent defense. The fixed effects regression also controls for the identity of the players in the games, so the regression is essentially comparing the performance of the same player in different conditions.

The results of the fixed effects regression further support the previous results that weather plays a significantly smaller role than opponent defense in the variation of fantasy performance of QBs and RBs. For the regression on the QB data, only wind speed shows up to be significant in the weekly fantasy points of the three weather elements, while temperature and humidity appear highly insignificant, with p-values larger than 0.5. Meanwhile, all three aspects of the passing defense are highly significant with p-values lower than 0.001. The magnitudes of the effects of opponent defense are stronger as well. A pass defense 10% worse than average in every aspect is expected to raise the QB’s fantasy points by 0.64 + 0.49 + 0.15 = 1.28 points. On the other hand, an increase of 10 mph in wind speed, a significant change, is only expected to lower the QB’s fantasy points by 0.73 points. For reference, playing at home raises a QB fantasy points by 0.64 points versus playing in an away game, on average.

For the regression on the RB data, only temperature shows up to be highly significant in the weekly fantasy points of the three weather elements while humidity appears to be moderately significant with a p-value around 0.05. Temperature appears not to be significant at all with a p-value larger than 0.5. Meanwhile, both aspects of the rushing defense are highly significant with p-values lower than 0.001. The magnitudes of the effects of opponent defense are stronger as well. A rush defense 10% worse than average in every aspect is expected to raise the RB’s fantasy points by 0.26 + 0.12 = 0.38 points. On the other hand, an increase of 20°F in temperature, a significant change, is only expected to lower the RB’s fantasy points by 0.34 points. For reference, playing at home raises RB fantasy points by 0.39 points versus playing in an away game, on average.

As can be seen from the analysis of weather and opponent defense, opponent defenses play a significantly more crucial role than weather conditions in impacting the weekly fantasy performances of QB and RB. While we should not completely ignore the weather when we decide on our starters for the week, it should be a minor point of consideration compared to opponent defenses.