February 17 – The American Association and the National League, along with the Northwestern League, sign the Tripartite Agreement (also known as the National Agreement). This agreement binds the leagues to respect each other's valid player contracts as well as increasing the size of the reserve list from 6 to 11 players. This leads to relative harmony among the leagues until the Players' League wars of 1889–1890.
March 14 – The Peoria Club of the Northwestern League makes a motion to ban blacks, a move directly aimed at Toledo's star catcher, Moses Fleetwood Walker. After heated discussion, the motion is withdrawn and Walker remains eligible to play.
April 15 – Francis Richter publishes the first issue of Sporting Life which will grow into the leading weekly publication for baseball information and run continuously until 1917.
April 24 – Terry Larkin, a pitcher who has not played in the majors since 1880, shoots his wife and a policeman, then tries to kill himself. He attempts suicide the next day and fails again. Both his wife and the police officer survive as well and Larkin will play in 40 games for the Richmond Virginians in 1884.
June 16 – The New York Gothams introduce ladies day, where all females are admitted free without restriction. This idea will remain a staple of major league baseball for nearly 100 years.
June 28 – Providence Grays player Joe Mulvey is shot in the shoulder while leaving the playing field at Messer Street Grounds in Providence. The shooter, James Murphy, was actually aiming for Mulvey's teammate, Cliff Carroll after Carroll had drenched Murphy with a hose. Within a month, Mulvey would be sold to the Philadelphia Quakers.
August 7 – The Providence Grays fall out of 1st place for good in their 6–4 loss to the Boston Beaneaters. For the 2nd straight season, Providence will lead the league for the majority of the season and not win the pennant.
August 11 – The Boston Beaneaters turn a triple play when catcher Mike Hines catches a muffed pop-up and catches the base-runners off guard.
August 11 – Fred Thayer, patent-holder for the invention of the catching mask, and George Wright sue Wright's former teammate Albert Spalding's sporting goods company for patent infringement. Spalding will ultimately be forced to pay Thayer royalties in the case.
September 6 – The Chicago White Stockings set a major league record by scoring 18 runs in the 7th inning in their 26–6 victory over the Detroit Wolverines. Tom Burns goes 3-3 with 2 doubles and a home run in the outburst, setting records for most extra-base hits and runs scored in one inning by a player.
November 22 – New York Gothams owner John B. Day proposes a resolution to prohibit a team from signing a player who has broken the reserve clause of his contract. This resolution, eventually adopted by both the American Association and National League, effectively changes the reserve clause from a device to protect owners from their own greediness to a vindictive weapon to be used against uncooperative players.
April 17 – John Bergh, 25, back-up catcher for the 1880 Boston Red Stockings.
July 5 – Charlie Guth, 27?, pitched a complete game victory in his only major league game in 1880 for the Chicago White Stockings.
September 21 – Dan Collins, 29, outfielder who played in 10 games from 1874–1876.
October 10 – Jim Devlin, 34, pitcher for the Louisville Grays in 1876–77 who led NL in games, innings, starts and strikeouts in its first season; expelled from baseball in 1877 due to a game-fixing scandal.