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.
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.
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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 Yomiuri, 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.
Impact of Travel Distance and Scheduling
Although NPB involves domestic travel, accumulated fatigue from long-distance trips affects visiting team performance. In the Pacific League, moves of approximately 1,500 km occur between the Nippon-Ham Fighters in Sapporo and the SoftBank Hawks in Fukuoka, sometimes requiring teams to play immediately after flights. MLB research has confirmed a tendency for visiting team run production to decline with greater travel distances, and a similar mechanism is presumed to operate in NPB. Additionally, when the schedule does not provide travel days between consecutive series, managing visiting starting pitcher conditioning becomes difficult, increasing bullpen reliance. Home teams commute from their residences to the ballpark, and freedom from such physical burden contributes to long-term winning percentage differentials.
Umpire Tendencies and Psychological Factors
One component of home advantage is the tendency of umpire decisions. Sports psychology research has proposed the social pressure hypothesis, which suggests that umpires unconsciously favor the home team when surrounded by loud crowd support. While pitch-tracking studies specifically analyzing NPB strike zone calls remain limited, the tendency for borderline pitches to be called in favor of home pitchers has been repeatedly confirmed using MLB pitch-tracking data. Additionally, some analysts note that home managers are in a more advantageous position when utilizing protests or the replay review system. On the player psychology front, experimental results indicate that home batters maintain confidence more easily when stepping to the plate backed by cheers, while visiting batters experience performance declines in hostile atmospheres.
Home-Away Performance Splits for Pitchers
When comparing NPB pitcher statistics between home and away games, many pitchers post superior numbers at home. Contributing factors include familiarity with the mound firmness and slope, the spatial relationship with the bullpen, and established warm-up routines. In particular, the difference between artificial turf and natural grass affects footing, requiring subtle landing timing adjustments that favor pitchers intimately familiar with their home park. Long-term trust relationships with catchers and shared sign systems also constitute home-specific advantages. From the batter's perspective, familiarity with opposing pitchers frequently faced at home offers an edge, while on the road batters encounter pitchers they have rarely faced, which tends to lower batting averages. These bidirectional effects accumulate to elevate overall home winning percentages.