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Is home field advantage a thing in 2020?

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A statistical examination of whether teams are better at home now than they have in recent years.

Kansas City Royals v Detroit Tigers Photo by Mark Cunningham/MLB Photos via Getty Images

Introduction

In 2007, the Serie A soccer league in Italy forced several of its teams to play in empty stadiums because of some serious fan misbehaviour. This provided people the opportunity to study home field advantage, which two economists from Sweden certainly did in this article published in 2010.

In short, they found that the lack of fans in stadiums took away referees’ natural tendency to call more penalties against away teams; if they called more against the home team, the crowd would let them hear it. There were other effects, too: more stoppage time added at the end of a half if the home team was behind, and so on. Fascinating stuff; a recent Sports Illustrated article examines this a little further.

So, here we are in 2020, with empty stadiums everywhere. Italian soccer sure isn’t Major League Baseball, but they both have officials who are humans (despite our calls for robot umps from time to time). Since humans are fallible creatures, I wanted to know if all those empty seats had an effect on home field advantage.

Hypothesis

The lack of fans in the stands, who would normally umpires to make calls that would favour the home team, would cause the home team to win fewer games than normal this season.

Method

I went to Baseball-Reference to gather the stats for all full seasons from 2010 through 2019, and then all 2020 games through August 23. Data from the detailed standings table were plugged into a spreadsheet, with the number of home wins extracted and summed. The winning percentage of home teams was calculated and graphed.

Results

From 2010-2019, the home team had a winning percentage, on average, of 0.5337. The standard deviation of these ten seasons was 0.00622. In a normal season, the total number of games is 2,430.

Caveats: From time to time, teams either play 161 or 163 games, with one fewer or one more home game. Also, a game in Baltimore during this time span was played in an empty stadium due to civil unrest in the city. There have also occasionally been teams playing in neutral sites (e.g Milwaukee) due to unusual weather situations. These should be statistically insignificant over the course of the over 24,000 games played over this time span.

For the 2020 season through August 23, there have been 406 games played so far, with the home team winning 225 of them, for a winning percentage of 0.5542.

Home team winning percentages, 2010 through August 23, 2020

Statistical Analysis

This is definitely not what I’d expected. In fact, using the standard deviation from the 2010-19 stretch, the 2020 home winning percentage is almost 3.3 SDs above the mean.

The 2020 home winning percentage is over 3 SDs from the mean.

Here, z = 3.29; if we assume the distribution of win percentages is randomly/normally distributed, that would put this season further off the mean than 99.90% of all expected MLB seasons (normal table from University of Arizona).

Conclusion

This season, home teams are winning an extremely unusually large number of games. The full season hasn’t been played yet, and there are definitely anomalies in how this season has played out so far, but with over 400 games played in 2020, this is very unusual.

Speculation

With this season being so strange, there’s probably any number of reasons why this phenomenon has been occurring. Here are some of my wild ideas:

  • If players are in their home city, they can follow a daily routine which is much more normal — even in 2020 — than they could ever have on the road. This could be at their own home/apartment/condo, at their home ballpark, or in transit between the two.
  • Travel away from one’s home ballpark is particularly stressful this year. Sure, everyone flies on private jets, but the process has got to be harder and more cumbersome these days.
  • Maybe there’s something going on with umpires this year, not unlike the Italian soccer referees. I can’t figure out why they would favour the home team even more without tens of thousands of potential enemies in the stands, though.
  • Ghosts.