Overview
A doubleheader is two games of the same matchup played on a single day. Under Rule 4.08 of the Official Baseball Rules (as amended for 2019) the second game may not begin until the first is complete, and it starts thirty minutes after the first game ends; even when a longer gap is needed, the interval between the two games may not exceed forty-five minutes. With the consent of both managers the second game may instead begin within thirty minutes of the first one finishing. Packing two games into one day with no rest day places a heavy physical load on players, above all on catchers who work both games in full gear and on pitching staffs that must cover two games' worth of relief work. Fans get two games in a single visit, but clubs absorb staffing and lighting costs for two games while gate revenue covers only one day, so the format is not efficient as a business.
In NPB
Doubleheaders were once written into the schedule for commercial reasons, but the last ones actually played in NPB were in October 1998, and none appears on the official 2026 schedule either. Neither the Baseball Agreement nor the Official Baseball Rules bans the format, so it remains available in principle; it simply has not been chosen, given the burden on players and the revenue math above. Games lost to rain are made up on separate dates instead, and the official 2026 schedule likewise handles postponements through reserve dates and other makeup slots. MLB, by contrast, has a practice of scheduling doubleheaders as rain makeups, and that is where Japanese fans mostly encounter the format.