The 1918 major league baseball season began on April 15, 1918. The regular season ended earlier than originally scheduled, September 2, because of a reduced schedule due to American participation in World War I. The National League and American League champions were the Chicago Cubs and Boston Red Sox, respectively. The postseason began with Game 1 of the 15th World Series on September 5 and ended with Game 6 on September 11. The Red Sox defeated the Cubs, four games to two, capturing their fifth championship in franchise history, since their previous in . Going into the season, the defending World Series champions were the Chicago White Sox from the season.
American League Opening Day took place on April 15 with four American League teams playing, the Philadelphia Athletics at Boston Red Sox, and the New York Yankees at Washington Senators, while National League Opening Day saw all eight teams play the following day. It was the first season since which saw the two leagues open on different days.
With World War I ongoing, a "work or fight" mandate was issued by the government, requiring men with non-essential jobs to enlist or take war-related jobs by July 1, or else risk being drafted. Secretary of War Newton D. Baker granted an extension to MLB players through Labor Day, September 2. In early August, MLB clubs decided that the regular season would end at that time. As a result, the number of regular-season games that each team played variedâÂÂ123 to 130 for AL teams and 124 to 131 for NL teams, including tiesâÂÂreduced from their original 154-game schedules. The final day of the regular season would see all teams but the Cleveland Indians and St. Louis Browns play. Later in August, Baker granted a further extension to allow for the World Series to be contested; it began on September 5 and ended on September 11. World War I would end two months later, with the Armistice of 11 November 1918.
10 tie games (6 in AL, 4 in NL), which are not factored into winning percentage or games behind (and were often replayed again) occurred throughout the season.
The postseason began on September 5 and ended on September 11 with the Boston Red Sox defeating the Chicago Cubs in the 1918 World Series in six games.
<section begin=Bracket/> <section end=Bracket/>
Any team shown in indicates a previous team a player was on during the season.
<sup>1</sup> American League Triple Crown pitching winner
<sup>2</sup> National League Triple Crown pitching winner
Robison Field of the St. Louis Cardinals is gradually referred to as Cardinal Field, after Helene Britton, daughter of the deceased former owner Frank Robison, sells her interest in the team following a deal in March 1917, ending the association between the Cardinals and the Robison family. By 1918, Cardinal Field became the name widely used.