Baseball is played in a range of temperatures. The coldest game in our database had an average temperature of 25 degrees and was played between the Twins and Orioles in April 2007. The hottest game since 2005 was played between the Diamondbacks and Marlins in July 2009, the average temperature that day was 110 degrees. How do hot and cold temperatures impact hitting?
The chart below shows the impact of temperature on hitting based on weather data from Baseball-Reference from 1990 to 2013.
As you can see batting average, slugging percentage and isolated power all increase as the temperature rises. If you assume this leads to increased scoring you are correct.
There is a direct correlation between rising temperatures and runs scored. There is more than a run difference between games played in temperatures below 50 degrees and games with temperatures over 90 degrees.
Average total and runs scored for all games since 2005
Of course, the oddsmakers are aware of the impact temperature has on run production. The average total for a game steadily increases as temperatures rise.
What might surprise some is that the average runs scored per game is greater than the average total per game at every temperature interval, yet for all games the win rate for the over is less than 50%. Why?
There is theoretically no ceiling on the runs two teams could score in a game and because an MLB game cannot be tied at least one run has to be scored for the game to end. Thus, the run differential for the “over” can be greater than the run differential for the “under” leading to a higher average of runs scored per game than average total.
We know rising temperatures influence runs scored. What impact does wind have on baseball totals?