The Nippon Professional Baseball (NPB) playoffs have taken several different forms throughout the organization's history. Japanese baseball is divided into two leagues; the Pacific League (PL) is less popular and less profitable than the Central League (CL). As a result, the PL has employed various playoff formats throughout its history in an effort to increase fan interest. The PL's first true playoff system was introduced in the 1973 season. It involved a split season plan that divided the season into two halves and the two teams that won each half went on to play each other in a five-game playoff series, with the winner advancing to the Japan Series. While popular with fans, the format was scrapped after ten seasons because of major issues and criticisms. In the year following their last split season, the PL returned to a single season, however if five or fewer games separated the first- and second-place teams at the end of the season, the two teams would play each other in a five-game playoff series. This playoff system was unpopular and ridiculed by media and fans. It only lasted three seasons with a playoff series never needing to be played.

A split season is a schedule format implemented in a variety of sports leagues. The season is divided into two parts, with the winners of both halves playing each other at the end for the overall championship.