Climax Series

History

Since the creation of the NPB's two-league system, the regular-season winner of the CL had always advanced to the Japan Series, where it competed against the PL champion. The PL used the same system until 1973, when the league created NPB's only postseason play prior to 2004 (other than the Japan Series). This system matched the team with the best first-half record against the team with the best second-half record. The winner of this best-of-five series advanced to the Japan Series, where they played against the CL champion. This system proved problematic when the Hankyu Braves won both the first and second halves of the 1976 and 1978 seasons, making a playoff series unnecessary. The system was eliminated after the 1982 season. Instead, the PL announced the following season that the first- and second-place teams would compete in a best-of-five playoff series after the 130-game regular season if five or fewer games separated the two teams. Unpopular with most baseball media and fans, the idea was scrapped after three seasons with a series never needing to be played. The two leagues returned to sending the team with the best regular season record in their respective league to compete against each other in the championship series.

Pacific League playoffs

In February 2003, the PL board of directors agreed to reintroduce a playoff system to be used for the 2004 NPB season. If a first-place team had a substantial lead in the standings nearing the end of the regular season, there was no pennant race and little excitement until the Japan Series began. The decision to add a PL playoff was an attempt to rectify this problem and increase the league's popularity. The new postseason plan initiated a two-stage playoff in which the top three PL teams competed. In Stage 1, the teams that finished the newly shortened, 135-game regular season with the second- and third-best records played each other in a best-of-three series. The winner of this series faced the league's top finisher in the second and final stage. The Stage 2 winner advanced to the Japan Series, where they competed against the CL's first-place team.

Originally, the top finisher in the league at the end of the season was supposed to receive home-field advantage throughout Stage 2, but in August 2003, PL officials announced that if the first-place team led the second-place team by more than five games at the end of the regular season, that team would also receive a one-game winning advantage in Stage 2's best-of-five series. For the 2006 season, PL officials removed the five-game lead requirement in favor of automatically awarding the first-place team the one-win advantage. In conjunction with this change, the first-place team no longer had home-field advantage for the entirety of Stage 2; instead, the remaining four games were to be split evenly between both teams' stadiums. This rule change became a non-factor after the eventual first-place Hokkaido Nippon-Ham Fighters clinched a Japan Series berth in two straight games.

During the three years of the PL's playoff system, the winner of the PL's postseason tournament competed against the CL team who finished the regular season with the best record. The disparity between the two leagues' postseasons provoked some criticism from baseball analysts. During the 2005 Japan Series, The Japan Times' Stephen Ellsesser called NPB's unbalanced postseason a "bad system" and believed that the CL's decision to not implement a playoff system of their own was "foolish". Citing the Hanshin Tigers' poor Japan Series performance, he speculated that the CL's lack of postseason play was a disadvantage. Ellsesser believed that the 17 days between their last regular-season game and the first Japan Series game did nothing to prepare the Tigers for the eventual championship series against the Chiba Lotte Marines, who had played continuously.

Climax Series creation

The CL had situational playoff scenarios written into its bylaws that required either a tie in the standings or a team with more wins finishing with a worse winning percentage than the top team, but a permanent playoff plan had never been created. In March 2006, encouraged by the success of the PL's playoff series, CL officials announced their intention to introduce postseason playoffs for the 2007 season to help boost declining attendance. During meetings held later that year, PL and CL officials disagreed over proposed plans detailing the new playoff system. Since the creation of the PL playoffs in 2004, the league awarded its pennant titles to the playoff winners rather than the team who finished the regular season with the best record. The PL disapproved of the CL's intentions to continue awarding their league title to the first-place finisher in the regular season while using the playoffs to determine which team would compete against in the Japan Series, as the PL had been awarding its pennant to its playoff champion.

In September 2006, both leagues agreed on a unified postseason system. The CL implemented a playoff system identical to the PL's, and the entire playoff series was dubbed the "Climax Series". The PL agreed to name the regular season first-place finishers league champions rather than the team that won the leagues' respective playoffs—a reversal from the previous three seasons. It was decided that both leagues would play 144 regular-season games, the first time both leagues would play the same number of games since the PL introduced its playoff system in 2004. The two leagues agreed that neither regular-season champion should receive a one-game advantage in Stage 2 of the Climax Series, claiming that it was unnecessary from a business point of view. This decision was overturned when each league awarded its champion a one-win advantage in Stage 2 starting with the 2008 Climax Series. At the same time, the series became a best-of-six series, where the first team to win four games advances to the Japan Series. This format has drawn some criticism, with some players describing the rule as "unfair", "bull" and "messed up", but it is still in use.

Current format

Both leagues employ the same two-series playoff format, with the top three teams from each league participating in their own two-stage playoff. If two teams vying for a third Climax Series spot finish the regular season with identical records, the team that finished the previous season with a better record is allowed to advance to the playoffs, unless if both teams finished with the same previous season record. This contrasts with Major League Baseball (MLB), which employs a one-game playoff, or other professional leagues that may use head-to-head season records (and further tiebreakers such as non-interleague play records, second half records, et al.). The first series, Stage 1, is a best-of-three series involving the regular season's second- and third-place finishers, with all games played at the second-place team's home field. The winner of this series goes on to face the league's pennant-winner in Stage 2. This series is best-of-six. The league champion is awarded a one-win advantage as well as home field advantage for the entire series, unlike most professional leagues where a 5-game playoff series runs 2-2-1 or 2-3 or a 7-game playoff series that runs 2-3-2 with the higher seed receiving the extra game. The winning teams advance to the Japan Series, where they compete against one another. Unlike MLB, NPB games may end in a tie if there is no winner after 12 innings of play. If a Climax Series game results in a tie, the win is credited to neither team. If this causes the series to end in a tie, the team who finished higher in the regular-season standings advances, unless if both teams finished with the same regular-season record. If both teams finished with the same regular season record, the team who won the most matches against the other team will advance.