A doubleheader is a set of two baseball games played between the same two teams on the same day in front of the same crowd. (The term originated in the railroad industry; see Double-heading.) In addition, the term is often used unofficially to refer to a pair of games played by a team in a single day, but in front of different crowds and not in immediate succession.
Today, a doubleheader is generally the result of a prior game between the same two teams being postponed due to inclement weather or other factors. Most often the game is rescheduled for a day on which the two teams play each other again. Often it is within the same series, but in some cases, may be weeks or months after the original date. On rare occasions, the last game between two teams in that particular city is rained out, and a doubleheader may be scheduled at the other team's home park to replace the missed game.
Currently, major league teams playing two games in a day usually play a "day-night doubleheader," in which the stadium is emptied of spectators and a separate admission is required for the second game. However, such games are officially regarded as two single games on the same date, rather than as a doubleheader. True doubleheaders are less commonly played, and usually are of the twi-night variety. Classic doubleheaders, also known as day doubleheaders, were more common in the past, but still are played at the minor league and college levels.
In 1959, at least one league played a quarter of their games as classic doubleheaders, which declined to 10% in 1979 and further to the point that there were eight years between the last two scheduled official doubleheaders. Reasons for the decline include clubs' desire to maximize revenue, longer duration of games, five day pitching rotation as opposed to four day rotation, time management of relievers and catchers, and lack of consensus amongst players.