How Much Effect Does Temperature Have On Home Runs

NathanPlot

Data plot from Dr. Alan Nathan’s article entitled “Global Warming and Home Runs: Is There a Connection?” showing the extra distance the ball travels at a specific temperature, relative to how far it would have traveled had the temperature been 72.7F

PITTSBURGHAccording to the Washington Post, the average global temperature in 2015 shattered 2014’s record-setting heat to become the hottest year since reliable record-keeping began.

While our current political climate (pardon the pun) has focused on this issue and its significance for many reasons, today we will look at it from a baseball perspective.

As everyone has come to understand, baseballs travel further in warmer weather. So it would stand to reason as the global temperature increases, so will the amount of runs/home runs in baseball.

Lets take a look…

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Per baseball-reference.com (via the Post), the average MLB game temperature during night games increased from 73.0 to 73.7 degrees from 2014 to 2015, and from 71.6 to 73.5 during day games

And while that number might seem insignificant as a whole, Dr. Nathan’s chart at the top of this post and quote below illustrates just how much the temperature can affect the distance a ball travels.

“Suppose the average MLB game-time temperature were 10F higher (than 72.7F). Fly balls on a typical home run trajectory would travel about 2.5 ft farther (about 0.6%), leading to 6% more home runs. As a more dramatic example, consider games played at the two extreme temperatures of MLB, 30F and 110F. The home run probability would be about 50% greater at the high end (110F) than at the low end (30F). This result simply confirms what everyone already qualitatively knows: balls carry better at higher temperatures, leading to more home runs.”

Digging deeper, Jeff Zimmerman looked at the average number of runs per game, relative to the temperature, in MLB from 2007 to 2013. We can see when the temperature was between 71 and 75 degrees, teams averaged 4.4 runs per game. When the temperature rose 20 degrees to between 91 and 95, the number of runs increased to nearly 5 per team.

ZimmermanPlot

Furthermore, Beyond The Box Score cobbled together all the numbers from 1990 – 2013, relative to temperature in 10 degree increments, from Baseball Reference and came up with this graph. As we can see once again, as the temperature rises, so do the amount of runs (as well as batting average, slugging, isolated slugging and home runs per at-bat).

BeyondBoxScore1

And finally, the Department of Math & Science at the University of Nevada-Reno put together a study featuring data from 22,215 MLB games, spanning the 2000–11 regular seasons, entitled, “The Impact of Temperature on Major League Baseball” and found this to be true:

The results show that, overall, offensive production is higher in warm temperatures compared to cold temperatures. Across all populations, runs scored, batting average, slugging percentage, and home runs show significant increases while walks show significant decreases in warm temperatures compared to cold temperatures. Additionally, the American League shows a much stronger impact of temperature on the statistics than the National League.

Consistent with past findings, home runs were most affected by temperature, increasing from 1.79 per game in cold temperatures to 2.35 per game in warm temperatures for away and home batters combined. Runs scored, which is arguably the most important statistic of a MLB game, showed the second strongest response to temperature in this study, increasing from an average of 8.95 per game in cold temperatures to 10.08 per game in warm temperatures overall. Home batters playing for the Oakland Athletics benefit the most from warm weather, where runs scored, batting average, slugging percentage, on-base percentage, and home runs all show significant increases in warm temperatures compared to cold temperatures. Away batters playing in Baltimore, Chicago’s Wrigley Field, and Kansas City should expect greater offensive production in warm weather as runs scored, batting average, slugging percentage, on-base percentage, and home runs increase significantly in warm temperatures at those stadiums compared to cold temperatures.” 

While MLB games are typically played during the warmer months of the year (April – October), the same can’t be said for college baseball, which typically starts its season in early to mid-February when most parts of the country are still covered in snow and ice.

And while this leads to some teams having to play 21 straight road games to open the season, most college baseball games take place well below the Mason-Dixon line until spring has officially sprung.

With this, we decided to attempt to take a small, early-season look at home run totals versus weather to see just how much of an affect it had on teams¹

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Mercer, who leads college baseball with 22 home runs through March 9th, have hit their home runs during games with an average temperature of 62.2 degrees²

Missouri State, who is tied for second in the nation with Pittsburgh with 21 home runs, have hit their home runs in games with an average temperature of 61 degrees, while Pitt has seen the temps at 67.6 degrees when they have gone yard.

N.C. State, with 20 team home runs, has hit the long ball when the temperature is 61.7 degrees. Illinois-Chicago, who are tied with the Wolfpack with the nation’s fourth-highest home run total, have gone deep in games where the temperature is 72.8.

One could look at these numbers and suggest Illinois-Chicago and Pittsburgh have benefitted the most from the relatively warmer weather. But with these two teams, another factor has perhaps played a larger role in each team’s home run total – the schedule.

In a three-game series against Texas Southern in to open the season, Illinois Chicago hit 18 of its 21 home runs. While the average temperature for the matchup in Houston was a robust 77.6 degrees in mid-February (and the Flames were probably very happy to be 942.3 miles from their home, considering the temps in Chicago the previous weekend were an average of 21 degrees), the opponent – and not the temperature – perhaps had more of an effect on the home run total in this instance.

For further proof, one would only need to look at UIC’s three-game series at No. 2 Vanderbilt the following weekend in which the Flames hit zero home runs in temperatures averaging 54.3 degrees.

Along those same lines, Pittsburgh took advantage of a three-game venture to Louisiana to face Grambling State, collecting 15 of their 21 home runs on the year in a three-game series against the Tigers.

When we look at each team’s Iterative Strength Ratings, we see Texas Southern comes in at No. 226 and Grambling State is No. 246, out of a composite of 261 teams. Meanwhile, Vanderbilt sits at No. 1, meaning Illinois-Chicago played one of the worst college teams in very hot weather and one of the best in fairly cold weather.

N.C. State has clearly done the best as a whole, playing in the second-coldest temps among the five teams, but also playing the second most difficult schedule. Mercer, who has collected home runs in 11 of its 13 games does not have a large outlier like Pitt or UIC and also boasts one of college baseball’s best players in Kyle Lewis – a Top-10 projected draft pick who is hitting .460/.591/.880 with 5 home runs, 17 runs and 17 RBI in 50 at-bats so far this season.

Missouri State’s Alex Jefferson has the honor of hitting a home run in the coldest temperature, going deep in 38 degree weather on Feb. 26 versus UConn in a game played in Clarksville, Tenn.

Ultimately, this limited data set does not allow us to make a definitive case of knowing if weather or team ability has a more profound effect on the amount of home runs hit in the early stages of the college baseball season. When the weather data becomes more accessible, we can certainly take a longer, more conclusive look at weather-influenced home runs

Strength of Schedule Rankings on March 9th, 2016: 

  • Illinois – Chicago: No. 38
  • N.C. State: No. 46
  • Mercer: No. 200
  • Missouri State: No. 207
  • Pittsburgh: No. 229

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Footnotes:

  1. While the data for home runs, runs per game and opponent strength of schedule is widely available, the data is fairly limited in terms of game temperature. The only way to access the game temperatures was through individual box scores, which for the purposes of this story became too time consuming. Moreover, some box scores did not provide the game temperature data. When this occurred, we looked at the temperature at the start of the game in the city the game was played, as provided by AccuWeather.com
  2. We looked only at the temperature in games each team hit a home run. So the average temperature referenced is the average in games in which a home run occurred, not a composite of overall temperature.