Is there a home-game advantage in professional sports?

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As I write this article, two pro sports leagues have recently concluded their seasons: the National Basketball Association (NBA) and the National Hockey League (NHL). In each league, there were surprises, with the Miami Heat making the NBA finals and the Florida Panthers making the NHL finals. Both of those Florida teams were eighth seeds in the playoffs, a spot which rarely leads to a place in the finals. For those unfamiliar with playoff formats for these leagues, an eighth seed means each of these teams had seven teams with better records in their respective conferences. Both the Heat and the Panthers had to win three playoff series, all of which required at least one win on the road.

So I wondered, does playing games at home matter? I pulled the data from the last 10 years for the four major U.S. sports leagues to see if there is an advantage to playing at home (data from sports-reference.com). The first thing I needed was a metric to judge performance at home. To do this, I looked at the home winning percentage and compared it to the overall winning percentage. In other words, how much does a winning percentage improve when games are played at home. Looking at the different leagues over the last 10 years, each league’s average is shown below:

As you can see, all the four leagues show an advantage when games are played at home, but that advantage varies from league to league. The NBA has the greatest advantage, while the NHL and Major League Baseball (MLB) have a much smaller advantage. Below is the ordered difference report, which shows that the differences between the leagues is statistically significant outside of the MLB and NHL.

One interesting thing about this data is that the variances between leagues are statistically different for the National Football League (NFL) than the other leagues. Below is a graph of the densities for each league:

As you can see the NFL has a lot more variability than the other leagues.  The most likely reason for this is the NFL has much fewer home games than the other leagues.  The NFL only plays 8 or 9 home games per season while the other leagues (NBA and NHL 41, MLB 82) play much more at least in non-covid years (we will get to that).  This to me is a nice illustration of the central limit theorem, which says the larger the population the more a distribution will look like a normal distribution. 

Since I mentioned it, you might be asking yourself what about the COVID year of 2020, when most games were played in empty stadiums. Did the home-game advantage decrease that year? I put that data together as shown in the graph below:

The home-game advantage during the pandemic varied for the four leagues. It was statistically significantly lower for the NFL and NBA, while the NHL showed no significant change during the 2020 pandemic season. Surprisingly, the MLB saw a statistically significantly improvement in home field advantage that year. The drop-off in home field advantage for the NBA and NFL is expected, indicating that fans have a positive impact on the home team. In fact, the NFL without fans showed no home field advantage at all.

For the MLB, I have a couple of thoughts on why this trend might exist. Each MLB ballpark is unique, with slightly different dimensions. As a result, the home team has a better understanding of how to play at their home field. While that explains part of the home advantage, I am not sure why it improved during the pandemic. Are fans cheering at the wrong time during MLB games? Does a quieter field improve communications, thus helping home teams? Given that the 2020 Astros had the greatest improvement at home when compared to any MLB team in the last decade, did the team go back to enhanced sign stealing with technology?

Comparing leagues is interesting, but what about individual teams? We can look at the data and see which teams enjoy the greatest advantage of playing at home. Below is a graph that allows you to use the filter to look at each league:

OK, the debate is clearly settled: the Packers, Hawks, Rockies, and Penguins have the best fans, which is why playing at home is such an advantage. However, before those fan bases start celebrating (and Packers fans start bragging to Bears fans about how hard it is to win at Lambeau Field), we need to remove the 2020 data to see the true impact of fans. Amazingly, removing the data from that pandemic season shows a different story, with the Vikings, Pacers, Rockies, and Flyers having the best advantage of playing at home. Apologies to Packers and Penguins fans who both got passed by a division rival.

But fans aren’t the only reason for why certain teams perform better at home. I live in Denver and the Rockies, Broncos, and Nuggets all enjoy a better than average home advantage (surprisingly, though, this doesn’t extend to the Avalanche). Clearly, Denver is home to the best fans in the country. Or is one reason for the improved home advantage due to the elevation in Denver? Denver, at a mile above sea level, has the highest elevation of any city that hosts pro sports teams in the U.S. The Denver teams most likely are better acclimated to playing in the more demanding conditions of higher elevation.

In summary, despite having two eighth seeds reach the finals in the NHL and NBA, there is an advantage to playing at home. That advantage might be fans, stadiums, weather, elevation, or even better sleeping conditions while at home. Whatever the cause, in professional sports, there is no place like home.