As I am writing this article there are two pro sports seasons recently came to an end in the States. The National Basketball Association (NBA) and the National Hockey League (NHL). Both seasons came to a somewhat surprising end 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 and made it to the finals. For those unfamiliar with playoff formats for these NBA and NHL this mean each of these teams had 7 teams with better records in their respective conferences. Both the Heat and the Panthers had to win 3 playoff series that all required at least one road win.
It made me ask the question does playing games at home mater? I pulled the data from the last 10 years for the 4 major US sports 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 that to the overall winning percentage. Basically, how much does your winning percentage improve when you play at home. Looking at the different leagues over the last 10 years here is the leagues average.
As you can see all the four leagues show an advantage of playing at home, but that advantage varies from league to league. With the NBA having the largest advantage and the NHL and MLB having a much smaller advantage. Below is the ordered difference report showing that the differences between the leagues is statistically significant outside of the MLB and NHL.
One interesting thing about this data is the variances between leagues are statistically different for the 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 advantage of playing at home decrease that year? I put that together and included the graph below.
The advantage of playing at home during the pandemic to empty stadiums in 2020 was statistically significantly lower for the NFL and NBA. The NHL showed no significant change during the 2020 pandemic season. Surprisingly the MLB saw a statistically significantly improvement in home field advantage in 2020. The drop off in home field advantage for the NBA and NFL is expected and indicates 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 a couple thoughts came to mind on why this trend might exist. Each ballpark in MLB is unique with slightly different dimensions and the home team has a better understanding of how to play at their home field. That explains part of the home advantage, but I am not sure why it improved during the pandemic. Are fans cheering at the wrong time during MLB games? Does improved communication help home teams? Did the Astros go back to enhanced sign stealing with technology? The 2020 Astros did have the largest improvement at home when compared to any MLB team in the last decade.
Comparing leagues is interesting, but what about individual teams? We can look at the data and see which teams enjoy the most advantage of playing at home. Below is a graph that you can use the filter to look at each league.
;
OK debate clearly settled the Packers, Hawks, Rockies, and Penguins have the best fans and that is why playing at home is such an advantage. Before those fan bases start celebrating, and Packer 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 that pandemic season shows a different story with the Vikings, Pacers, Rockies, and Flyers having the best advantage of playing at home. Apologies to Packer and Penguin fans who both got passed by a division rival.
There are other explanations outside of fans 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 not the Avalanche). Clearly, Denver is home to the best fans in the country or part of the improved home advantage could be due to the elevation in Denver. Denver at a mile above sea level has the highest elevation of any city on that hosts a pro sports team in the USA.
In summary, despite this year’s results in having eight 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 at home. Whatever the cause in professional sports there is no place like home.
