The 1888 major league baseball season began on April 18, 1888. The regular season ended on October 17, with the New York Giants and the St. Louis Browns as regular season champions of the National League and American Association, respectively. The postseason began with Game 1 of the fifth World's Championship Series on October 16 and ended with Game 10 on October 27, in what was a best-of-eleven-playoff. The Giants defeated the Browns, six games to four, capturing their first World's Championship Series.
Over the offseason, the American Association's New York Metropolitans folded, and saw them replaced by the newly enfranchised Kansas City Cowboys. Meanwhile, the Brooklyn Grays renamed as the Brooklyn Bridegrooms.
The 1888 schedule consisted of 140 games for all teams in the American Association and National League, each of which had eight teams. Each team was scheduled to play 20 games against the other seven teams of their respective league. This continued the format put in place by the American Association since the season and was the first season that the National League adopted the format. This format would last until .
American Association Opening Day took place on April 18 featuring all eight teams, while National League Opening Day took place on April 20, also featuring all eight teams. The American Association would see its final day of the regular season on October 15 with a game between the Cleveland Blues and Philadelphia Athletics, while the National League would see its final day of the season on October 13, featuring all eight teams. The 1888 World's Championship Series took place between October 16 and October 27.
The 1888 season saw the following rule changes:
An asterisk (*) denotes the ballpark a team played the minority of their home games at
Blue laws restricted Sunday activities in several localities, causing several teams of the American Association (which was informally referred to as the "Beer & Whiskey League" due to its openness on alcohol, compared to the National League) to play at ballparks in a different locality.
21 tie games (9 in AA, 12 in NL), which are not factored into winning percentage or games behind (and were often replayed again), occurred throughout the season.
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Any team shown in indicates a previous team a player was on during the season.
<sup>1</sup> National League Triple Crown pitching winner
The Kansas City Cowboys join the American Association and play at Association Park in Kansas City, Missouri. For the last home game of the season, they permanently left Association Park and move into Exposition Park on September 30.
The New York Giants would play their final game at the original Polo Grounds in game 5 of the World's Championship Series on October 20 against the St. Louis Browns, playing at Oakland Park in Jersey City, New Jersey, St. George Cricket Grounds in St. George, New York, and the second Polo Grounds further uptown the following season.
The South End Grounds, home of the Boston Beaneaters, saw a completely new structure over the offseason. The team would play their first game at the revamped South End Grounds on May 25.
Three teams of the American Association hosted Sunday games: