February 8 – Demolition crews begin the dismantling of the Polo Grounds in order to run new streets through the property. The New York Giants will be forced to play their home games at the St. George Cricket Grounds until a new Polo Grounds is finished in early July.
March 7 – Pittsburgh Allegheny players, Bill Kuehne and Ed Morris, are arrested and charged with operating a gambling house out of their billiard parlor. The charges against both are dropped when the prosecution's star witness fails to appear in court to testify against them.
March 20 – A New York City sporting goods house receives an order from Japan for baseball equipment. The corresponding letter states that a league will soon be formed as the game has been played there for several months already.
May 2 – Yank Robinson of the St. Louis Browns is fined and suspended after getting into a shouting match with Browns owner Chris von der Ahe. His teammates nearly refuse to make a trip to Kansas City and do lose three straight games to the Cowboys amid suspicion they are throwing the games because of Robinson's suspension.
May 14 – The Pittsburgh Alleghenys suspend pitchers Ed Morris and Pete Conway, so they will not have to pay the salaries for the two sore-armed pitchers. Morris will return in three weeks although he will never again be an effective pitcher while Conway, a 30 game in 1888, will never pitch again.
May 19 – Most of the seating is destroyed by fire at Brooklyn's Washington Park. The stands will be rebuilt within a month.
June 11 – Dan Brouthers strikes out in a game for the first time this season. Brouthers will end the year with only six strikeouts in over 550 plate appearances.
June 13 – After the Louisville Colonels lose their 19th straight game, owner-manager Mordecai Davidson threatens to fine each player $25 if they lose their next game, even though the players are already owed back pay by Davidson.
June 17 – After consulting Baltimore manager, Billy Barnie, the striking players of the Louisville Colonels return to the field for a doubleheader. The Colonels blow a ninth inning 6–3 lead in Game 1 to lose and manage only one hit while committing seven errors to drop the second game.
June 19 – Center fielder Dummy Hoy sets a major league record by throwing three runners out at the plate in one game.
June 22 – The Sporting News reports that major league players are unhappy with the classification system for pay and no say or share in their sale to other clubs, and that a strike is imminent beginning in early July.
July 8 – The New York Giants play their first game at the newly relocated Polo Grounds. The stadium will remain a fixture in major league baseball until its demolition in 1964.
July 12 – John Clarkson of the Boston Beaneaters is taken out after pitching five innings of no-hit ball in order to rest him for his next start. His teammate, reliever Bill Sowders, allows one hit over the last four innings for the combined one-hitter.
July 14 – Albert Spalding publishes his ideas for the classification and structure of the minor leagues. His ideas will be the foundation of minor league baseball that last to the present day.
July 26 – Jay Faatz hits possibly the shortest grand slam ever when he hits a ball that ricochets off of the third baseman's foot and rolls under some temporary bleachers placed close to third base. Faatz circles the bases as the ball is still in play according to the park's ground rules.
July 29 – Mike ″King″ Kelly of the Boston Beaneaters robs the Philadelphia Quakers of a victory when, after Sam Thompson had apparently hit a long drive over the right field fence for a home run, he manages to throw a ball back into the infield that holds Thompson on the bases. While the Quakers argue that Kelly used a different ball, the umpire rules it is the game ball and allows the play to stand. Thompson is stranded on base as the Beaneaters go on to win 7–6 in extra innings.
September 3 – Con Daily of the Indianapolis Hoosiers makes the final out in a 7–6 loss to the Boston Beaneaters just after the umpire had apparently called time. Given a second chance, Daily hits a two-run single to give the Hoosiers an 8–7 win.
September 7 – In a critical two-game series, the St. Louis Browns leave the field in Brooklyn in the ninth inning leading 4–2 claiming it is too dark to continue play. Umpire Fred Goldsmith disagrees and forfeits the game to the Brooklyn Bridegrooms. Several Browns players are hit by thrown bottle as they leave the park.
September 8 – Citing safety concerns, the Browns fail to show for their game against Brooklyn and forfeit for the second day in a row, giving the Bridegrooms a 4½ game lead over the Browns.
September 11 – In a season that will have 135 rainouts between the two leagues, every scheduled game in both leagues is postponed due to rain on this day.
September 27 – Out of the pennant race, the Philadelphia Quakers make a largely symbolic move by releasing Brotherhood activists outfielder George Wood, who is batting .251, and pitcher Dan Casey, who has a 6–10 record.
October 5 – The New York Giants clinch the National League pennant on the last day of the season with a 5–3 win coupled with the Boston Beaneaters 6–1 loss. It was the first time in major league history that the pennant was determined on the last day of the season.
October 6 – The Brooklyn Bridegrooms complete their home schedule with a 9–0 victory. Brooklyn sets a new National League season attendance record by drawing 353,690 fans in a season.
October 19 – The Giants even the series by taking Game 2 by a score of 6–2.
October 22 – The Bridegrooms take Game 3 by a score of 8–7 in a game called because of darkness that ends with the Giants having the bases loaded and one out in the top of the ninth inning.
October 23 – In another game called early by darkness, New York scores five runs in the top of the sixth inning to tie the game at seven, only to see the Bridegrooms win it on a three-run homer by Oyster Burns in the bottom of the sixth.
October 24 – The Giants win Game 5 by a score of 11–3.
October 25 – New York evens the series at three games apiece by tying the game at 1 with a run in the ninth inning. The Giants then win it in the 11th inning as Hank O'Day outlasts Adonis Terry in the 2–1 extra inning thriller.
November 21 – The National League issues its reply to the Players' League manifesto. Claiming that the League saved baseball in 1876 and that under the reserve rules players' salaries had "more than trebled", the NL denounces the Brotherhood movement as "the efforts of certain overpaid players to again control [baseball] for their own aggrandizement. . . to its ultimate dishonor and disintegration."