The Overall Picture of Home Advantage
The home team winning percentage in NPB has historically ranged from approximately .530 to .540 over the long term. While this is slightly lower than MLB's approximately .540, a statistically significant home advantage clearly exists. Comparing the Central and Pacific Leagues, the Pacific League tends to have a slightly higher home winning percentage, possibly influenced by home ballpark characteristics and the cheering culture of Pacific League fans. Data from the 2000s onward reveals an interesting trend where home advantage in interleague play is greater than in regular league games, likely because lower frequency of matchups makes it harder for visiting teams to adapt.
Ballpark Characteristics and Home Winning Percentage
Differences in home advantage magnitude are observed between dome and outdoor stadiums. In enclosed dome stadiums such as Tokyo Dome and Kyocera Dome, the home team's environmental adaptation advantage is limited since weather has no impact. Conversely, at outdoor venues like Koshien Stadium and Yokohama Stadium, home teams familiar with wind patterns and temperature changes often gain an edge. Koshien's sea breeze is particularly known for suppressing right-handed hitters' home runs, and Hanshin Tigers pitchers factor this wind into their pitch selection. MAZDA Zoom-Zoom Stadium Hiroshima is known for being filled with Carp fans, serving as a prime example of how crowd support amplifies home advantage.
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Correlation Between Attendance and Home Winning Percentage
A weak but positive correlation exists between attendance figures and home winning percentage. The cheering generated by a full crowd provides psychological support for home team players while creating pressure on visiting teams. The spectator-free games during the 2020 COVID-19 pandemic served as a natural experiment to test this hypothesis. Home winning percentage during the spectator-free period dropped to approximately .510, showing a clear difference from the normal rate of around .535. These results suggest that spectator presence is an important component of home advantage. However, since spectator-free games also involved changes in travel burden and routine disruptions, isolating the crowd effect alone remains difficult.
Home Advantage in the Japan Series
In the Japan Series, home advantage becomes even more pronounced than during the regular season. Over the past 30 years, the home team winning percentage in the Japan Series has reached approximately .560, exceeding .600 when limited to Game 7. This is thought to result from the amplified advantage of playing in familiar surroundings amid the heightened tension of a short series. In the 2013 Japan Series between the Rakuten Eagles and Giants, Rakuten won all their home games at Kobo Park Miyagi, maximizing home advantage to achieve the franchise's first championship. Since the introduction of the Climax Series, the system granting home-field rights to the regular season first-place team has also served to enhance the value of the pennant race.
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