January 3 – Frank J. Farrell and Bill Devery pay $18,000 for the defunct American League franchise in Baltimore and relocate the team to New York and called them the Highlanders. The Highlanders would years later receive a new team name and become the New York Yankees.
January 13 – Win Mercer, recently appointed player-manager of the Detroit Tigers, commits suicide on January 13, 1903 in San Francisco during a barnstorming tour. Mercer reportedly had a gambling problem.[4]
May 6 – The Chicago White Stockings committed twelve errors, and the Detroit Tigers answered back with six of their own. The combined "18-E debacle" set a modern Major League record for the most errors (by two teams) in a single game.
June 25 – Wiley Piatt of the Boston Beaneaters became the only pitcher in the 20th century to lose two complete games in one day. Piatt allowed fourteen hits, while striking out twelve, en route to 1–0 and 5–3 St. Louis Cardinals victories.
July 1 – Cy Young drives in the lone run to lead Boston to a 1–0 victory over Chicago.
July 2 – Jack Doscher, a pitcher for the Chicago Cubs, becomes the first son of a former major league player to play in the majors. His father, Herm Doscher, played from 1872–1882 as a journeyman outfielder/infielder.
August 17 – The Detroit Tigers release second baseman Heinie Smith, whom they acquired via trade prior to the start of the season.
September 3 – Cleveland Naps rookie Jesse Stovall tosses an 11-inning shutout, 1–0, over the Detroit Tigers. The feat still remains as the longest shutout ever for a major league pitching debut.
January 12 – Win Mercer, 28, pitcher for four teams from 1894 to 1902, who posted two 20-win seasons and led the National League in games started, shutouts, and saves in the 1897 season.
January 13 – Pete Conway, 36, pitcher who posted a 61–61 record for four teams from 1885 to 1889.
February 6 – Hardie Henderson, 40, pitcher who went 81–121 with four teams between 1883 and 1888.
March 19 – John Conkey, 83, Boston businessman who co-founded the Boston Red Stockings of the National Association, predecessor of the modern Braves franchise, in 1871 and served as its president in 1871–1872.
July 2 – Ed Delahanty, 35, slugging left fielder since 1888, a three-time .400 hitter who ranked second only to Cap Anson in career hits; died after falling from a railroad trestle crossing the Niagara River.
^ abcdefghijklmnopqrstRichter, Francis C, ed. (1904). "Southwest Washington League". The Reach: Official American League Baseball Guide. Philadelphia, Pennsylvania: A. J. Reach Company. Retrieved August 29, 2018.
