Interleague play (NPB)

Sponsored by Suntory, the Suntory Cup was a preseason interleague tournament created to serve as a test run for regular-season interleague play. It was held only twice, once before the 1999 and 2000 seasons. The tournament consisted of a series of exhibition games between CL and PL teams. After each team played one game against all six teams in the other league, the team with the highest winning percentage was declared the winner. All of the games featured the designated hitter rule and any game tied at the end of nine innings resulted in a draw. Among other payouts, the winning team received ¥10 million of the ¥34.6 million purse and the most valuable player of the series took home ¥2 million.[4]

Talk of introducing interleague play as regular season games emerged again before the 2004 season. In February, Keio University professor Masaru Ikei wrote an op-ed in the Sankei Shimbun detailing proposals that would help revive Japanese baseball; interleague play was his first idea. A few weeks later, Commissioner of Baseball Yasuchika Negoro expressed interest in exploring the idea of in-season interleague games and was willing to discuss the idea with general managers and team owners.[3]

During the 2004 Nippon Professional Baseball realignment, the planned merger of two PL teams, the Kintetsu Buffaloes and the Orix BlueWave, along with the rumor of a second PL team merger in the near future prompted talk of possibly contracting and restructuring the two-league system into one ten-team league.[5] If NPB was restructured in this way, every team would be playing every other team throughout the regular season.[6] Instead of this restructuring, Hanshin Tigers' president Katsuyoshi Nozaki proposed interleague play as a possible alternative solution. He claimed that interleague play would allow Central and Pacific League teams to play each other an equal number of times so that it would seem that it was a one-league system, however the All-Star Series and the Japan Series, two series played between teams and players from the opposing leagues, could be saved.[7] Eventually, team representatives approved the merger between the Buffaloes and BlueWave but also agreed to maintain the two-league system while still looking into introducing interleague games for the next season.[8] During an owners meeting on September 29, 2004, a plan was approved to hold interleague regular-season games during the 2005 season.[9]

Nippon Professional Baseball first implemented regular-season interleague games in the 2005 season. Thirty-six interleague games were played by all twelve teams during a single six-week block between May 6 and June 16 and the event was sponsored by Nippon Life. Each team in the Central and Pacific Leagues played three home and three away games against each club from the opposing league. All series during this period consisted of three games. For any weekend rainouts in any outdoor ballparks, Mondays served as makeup days. The four days between the end of interleague play on June 16 and resuming the regular intraleague schedule on June 21 were left open to accommodate any additional makeup games.[6]

After two seasons, the number of interleague games played by each team was reduced from 36 to 24.[10] CL representatives pushed for a reduction in games because they believed that the four off days needed to potentially replay postponed games were too many.[11] Each of the twelve series was reduced from three to two games.[10] For only the 2014 season, the 10th season featuring interleague play, NPB inverted the designated hitter rule. Instead of the designated hitter being used in games where the Pacific League team was the home team, it was in effect in Central League parks.[12] Later that same season, it was announced that the interleague schedule would again be changed for a third time starting with the 2015 season. Again, the CL was unhappy with the interleague schedule. They cited the frequent travel required for the shorter two-game series of the 24-game format as the reason for the change. CL officials used the increased frequency of games being played by the Japan national baseball team as leverage in the negotiations, and argued that the international competitions required a more efficient NPB schedule. Interleague play was again reduced, this time from 24 to 18 games for each team.[11] Due to the COVID-19 pandemic, NPB decided to cancel interleague play for the 2020 season. The cancellation marked the first time since its inception in 2005 that interleague games would not be held and was an effort to maximize the number of intraleague games that could be played during the shortened season.[13] Cancellations and modifications of both the All-Star Series and Climax Series were also eventually announced for the same reasons.[14]