Old Hoss Radbourn won a record 60 games (some sources have revised the total down to 59), a record that likely will never be exceeded. In addition to wins, Radbourn led the National League in games (75), games started (73), complete games (73), ERA (1.38), saves (2), strikeouts (441), and innings pitched (678.2).
February 18 – Terry Larkin, recently released from prison after shooting his wife and a police officer in 1883, is arrested again for threatening to shoot his father. Larkin will be released and play this season for the Richmond Virginians. Larkin will later be institutionalized after challenging his former employer to a duel and will commit suicide by slitting his throat with a razor in 1894.
March 4 – The National League reduces the number of balls needed for a walk to six. Team owners agree to provide two separate benches for the teams in order to cut down on player fraternizing during games.
March 15 – Henry Chadwick writes in a newspaper column that a ground-keeper in St. Louis has started placing tarpaulins over the bases when it rains in order to keep them dry. Other clubs will follow suit and cover the pitching area and batter areas as well.
May 1 – Moses Fleetwood Walker becomes the first black to play in the major leagues. Walker will play in 42 games for the Toledo Blue Stockings, have 152 at-bats and get 40 hits in his only season in major league baseball. Facing racism constantly, even his own teammates refuse to play with him. An injury in mid-July effectively ends Walker's season and he is later released. No other African-American will play in the major leagues until Jackie Robinson in 1947.
May 1 – The Cincinnati Red Stockings of the American Association has a section of their stands collapse as fans are leaving the park following their opening day game. There are numerous injuries and one fatality in the collapse.
May 29 – The Chicago White Stockings hit 5 over-the-fence home runs in their home opener against the Detroit Wolverines. The White Stockings new ground rule allows a home run instead of a double for any ball hit in the air over the 180' left field fence or the 215' right field fence. After Chicago increases their home run output from 13 in 1883 to 142 this season, the National League will mandate a minimum fence distance of 210 feet beginning in 1885.
June 28 – While playing a Sunday game in Toledo, the players are arrested in the 6th inning for violating the city ordinance banning Sunday baseball. Due to the unruly crowd, the police allow the players to complete the game. The Brooklyn Atlantics defeat Toledo 5–3 before players from both teams are taken into custody.
July 28 – Charles Radbourn gains a victory in relief for the Providence Grays in the game that provides the point of contention as to whether Radbourn won 59 games or 60 in 1884. The Grays were trailing 4–3 when starting pitcher Cyclone Miller finished pitching the bottom of the 5th inning. Providence scored 4 runs in the top of the 6th to take the lead, then Radbourn came in to pitch starting in the bottom of the 6th. Under the scoring rules of the day, Radbourn was credited with the win. Miller would have gotten the victory under today's scoring rules, hence the discrepancy in total wins for Radbourn.
August 5 – Thomas Lynch, a deaf-mute, makes his major league debut for the Chicago White Stockings in the pitcher's box and is winning until he tires in the eighth inning. Cap Anson, who had hit two homers in the game, relieves him and promptly loses 8–5. Lynch will never appear in another major league game.
August 6 – Cap Anson hits three home runs in a 13–4 win, giving him five homers in his last two games.
September 15 – Manager Joe Simmons of the Wilmington Quicksteps pulls his team off the field before a home game against the Kansas City Cowboys when he realizes he will be unable to pay the required $60 gate fee to the visiting Cowboys as the attendance is zero. The visiting Cowboys are 7–55–2 (.112) while the Quicksteps are 2–16 (.111) and occupy the cellar in the Union Association standings; following this, the Quicksteps drop out of the Association and disband.
October 4 – In his first start since his no-hitter on September 28, Ed Cushman takes another no-hitter into the 9th inning only to give up a bloop single and finish with a 1-hitter.
October 4 – Sam Kimber of the Brooklyn Atlantics pitches a 10 inning no-hitter that ends in a 0–0 tie after the game is called because of darkness.
October 5 – Charlie Sweeney and Henry Boyle of the St. Louis Maroons combine on a 5 inning no-hitter when the game is called on account of rain. Despite the no-hitter, the Maroons lose 1–0 when 2 errors allow the only run of the game.
November 20 – The National League votes to allow overhand pitching for the 1885 season, although there are restrictions placed on the delivery in order to keep velocity down. In addition, teams are now required to supply a separate bench for each club at their park to limit inter-team fraternization.