Post-season playoff: Chicago White Stockings played St. Louis Browns. Series ended with both teams going 3–3–1 in a best-of-7 series. Game 1 ended in a tie called after 8 inning due to darkness; Game 2 was awarded to Chicago by forfeit after 6 innings because St. Louis refused to continue after disputing an umpiring decision. Both teams dispute series and claim championship.
June 17 – "Phenomenal" Smith loses his first start as a Brooklyn Gray by a score of 18–5 after his teammates commit 14 errors behind him, including 7 by shortstop Germany Smith. "Phenomenal"'s boast of being so good that he could win by himself doesn't sit well with the other Brooklyn players, who are fined $500 for their intentional poor play. In the interests of team chemistry, Smith is immediately released.
June 25 – 10 different players collect at least 2 hits each for the Brooklyn Grays in their 21–14 win over the Philadelphia Athletics. George Strief of Philadelphia sets a major league record by hitting 4 triples in the game.
July 4 – Owen Keenan of the Youngstown, Ohio club beats New Castle in both games of a double-header, pitching one game right-handed and the other game left-handed.
July 11 – After winning 175 games while pitching over 2,300 innings for the Chicago White Stockings since 1880, pitcher Larry Corcoran is released after straining his arm muscles so badly that he is unable to throw. Corcoran will only pitch 54 more innings and win 2 more games for the remainder of his career.
October 7 – Fred Shaw of the Providence Grays throws a 5 inning no-hitter before 12 fans in Buffalo in the first game of a double-header against the Bisons. Shaw beats them again in another 5-inning game in the nightcap.
October 10 – The Providence Grays sweep the Buffalo Bisons in a double-header in the Bison's last day in the major leagues. Buffalo finishes the season with a 17-game winless streak, only managing 1 tie in the season's last 3 weeks.
October 10 – Joe Gerhardt, second baseman of the New York Giants finishes the season with a .155 batting average while shortstop Charlie Bastian of the Philadelphia Quakers ends the year with a .167 average. Both players set still-standing records for the lowest batting average in a season (with a minimum of 350 at-bats) for their respective positions.
October 17 – The National League sets a minimum player salary of $1,000 and a maximum of $2,000 for the 1886 season.
October 22 John Montgomery Ward, along with several teammates, forms the Brotherhood of Professional Base-ball Players, the first union in professional sports history. The Brotherhood would ultimately result in the Players' League in 1890.