The 1884 major league baseball season began on April 17, 1884. The National League and American Association's regular seasons ended on October 15, with the Providence Grays and New York Metropolitans as the NL and AA pennant winners, respectively. The newly founded Union Association regular season ended on October 19, with the St. Louis Maroons as the UA pennant winner. The postseason between the AA and NL began with Game 1 of the first World's Championship Series (the first inter-league championship game of its kind in the Major Leagues) on October 23 and ended with Game 3 on October 25, in what was a best-of-five-playoff. The Grays swept the Metropolitans in three games, capturing their first World's Championship Series.
Prior to the 1884 season, in September 1883, the Union Association was formed, in direct contravention to the reserve rule (that a ballplayer could be reserved by a team) of the 1883 National Agreement (a.k.a. Tripartite Agreement) signed between the National League, American Association, and minor league Northwestern League. In response to formation of the UA, the AA expanded their league from an eight teams to twelve teams to undermine the weak footing the UA had, as UA teams were mostly in cities that already had established AA and NL teams.
The American Association expansion saw the minor league Brooklyn Grays of the Inter-State Association of Professional Baseball Clubs join as the Brooklyn Atlantics (today's Los Angeles Dodgers) and the Toledo Blue Stockings join from the minor league Northwestern League, as well as the establishment of the Indianapolis Hoosiers and Washington Nationals. The latter played their last game on August 2, and were replaced by the minor league Eastern League's Richmond Virginians to finish Washington's schedule.
The Union Association was largely unstable throughout its only year in existence (though confidence in the league remained high), as three of its founding teams would not make it to the end of the season. The Altoona Mountain Citys folded on May 31, and were replaced by the Kansas City Cowboys on June 7. The Philadelphia Keystones folded on August 7, and were replaced by the Eastern League's Wilmington Quicksteps. The Chicago Browns relocated to Pittsburgh as the Pittsburgh Stogies following their August 21 game. The Quicksteps would fold on September 15, while the Stogies would fold just three days later. On September 27, the Milwaukee Brewers and St. Paul Apostles (now renamed the St. Paul Saints) were recruited from the Northwestern League to finish the Philadelphia / Wilmington and Chicago/Pittsburgh schedules, respectively.
The 1884 season featured the second African American player in the major leagues (following William Edward White five years prior), debuting May 1 and playing 42 games for the Toledo Blue Stockings of the American Association. During his tenure, he faced abuse from other players (including teammates), fans, and the press, and even threats of being mobbed by 75 men before a road trip to Richmond, Virginia, before being released due to injury on September 29, prior to the road trip. His brother Weldy Walker played on the Toledo Blue Stockings for five games between July and August, becoming the third African American in the major leagues.
While it wouldn't be until that the color barrier was formally implemented (thanks to threats to not play from Chicago White Stockings manager Cap Anson and the general racism in society), the color barrier would not begin breaking until the Brooklyn Dodgers called up Jackie Robinson in , 63 years after Walker's last game.
The 1884 schedule consisted of 110 games for all teams in the American Association, which had twelve active teams, and 112 games for all teams in the National League and Union Association, each of which had eight active teams. Each AA team was scheduled to play 10 games against the other eleven teams in their league, and each of NL & UA teams were scheduled to play 16 games against the other seven teams of their respective league. The National League increased its total games per team from 98 to 112, 14 games to 16 games per seven opponents. The new Union Association copied this format. Meanwhile, the American Association, expanding from eight to twelve teams, changed from the 98-game format to the 110-game format. The National League would continue to use their 112-game format through the following season, while the American Association would copy the NL format.
Union Association Opening Day took place on April 17 featuring six teams, while American Association and National League Opening Days took place on May 1, featuring all twelve and all eight teams, respectively. The Union Association would see its final day of the regular season on October 19 featuring four teams, while the American Association and National League would see their final day of the regular season on October 15 featuring all twelve teams and four teams, respectively. The 1884 World's Championship Series took place between October 23 and October 25.
The 1884 season saw the following rule changes:
An asterisk (*) denotes the ballpark a team played the minority of their home games at<br> A dagger (â ) denotes a team that folded mid-season<br> A double dagger (â¡) denotes a team joined mid-season
Four teams played in four neutral or alternate sites in which they were treated as the home team. Meanwhile, blue laws restricted Sunday activities in several localities, causing the Indianapolis Hoosiers 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.
35 tie games (19 in AA, 10 in NL, 6 in UA), 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.<br> Any team shown in italics indicates a team a player was on from a different league. Any stat from said different league is not calculated to determine the league leader.
<sup>1</sup> American Association Triple Crown pitching winner
<sup>2</sup> National League Triple Crown pitching winner<br> <sup>3</sup> All-time single-season wins record
The 1884 season saw the single-season Union Association form, and with it, there were initially eight new teams in eight venues:
Four of these teams folded, one of which relocated cities prior to folding. All four were replaced with other teams who played in different venues:
The 1884 season saw the American Association with two new teams:
The 1884 season saw four teams relocate to new ballparks:
For various reasons, three teams would play home games at neutral sites:
The Indianapolis Hoosiers hosted 11 Sunday games at the Bruce Grounds north of Indianapolis city limits in Center Township on May 18, 25, June 22, 29, July 6, 13, 20, August 3, 10, 31, and September 21.