1st After having led the AA race all season except for 3 days in April, St. Louis falls to 2nd place behind Brooklyn after losing to Columbus, 6–5, on a 10th-inning HR by Dave Orr.
2nd In the afternoon game of a Labor Day doubleheader in Boston, Hardie Richardson hits a leadoff homer and P John Clarkson (36-13) makes it stand up for a 1–0 win over Indianapolis. Henry Boyle takes the loss.
3rd Indianapolis (NL) gets a last-second reprieve in the 9th inning when the ump calls time just before Con Daily apparently makes the last out of the game. Batting again, Daily singles home 2 runs to cap a 6-run rally to beat Boston, 8–7.
4th Brooklyn maintains its 1.5 game lead in the AA as they beat up on Cincinnati, 12-1 Tom Lovett connects for a 4th inning grand slam off Mike Smith.
6th Three walks off Silver King and an error by 2B Robinson hand the game to the Orioles as the slumping Browns (AA) lose again, 3–2, in 7 innings. King will end the year with a 34–17 record, while teammate Elton Chamberlin will finish at 34–15 (both these numbers are revised figures after research in 2002 by historian JP Caillault. These numbers were accepted by 19thcentury historian David Nemec).
7th In the most controversial game in AA history, the Browns walk off the field in Brooklyn while leading 4–2 in the 9th inning. They claim it is too dark to play, but the lighted candles in front of their bench by owner Chris Von der Ahe make umpire Fred Goldsmith determined to finish the game no matter what. Several St. Louis players are hit with bottles as they leave the grounds.
8th Claiming they cannot count on their personal safety, the Browns fail to show up for the scheduled Sunday game with the Bridegrooms at Ridgewood. The forfeit pushes the Browns 41⁄2 games behind.
10th Batting for Hank O’Day, New York Giants pitcher Mickey Welch strikes out as the first pinch hitter in ML history. This must have been an injury situation since a rule allowing pinch batters in non-injury situations will not be instituted until 1892. The first pinch hitter under that rule is generally agreed to be Jack Doyle, on June 7, 1892.
11th Rain prevents every scheduled game in both ML leagues. For the season the NL will have 62 rainouts and the AA 73.
12th Clarkson pitches and wins both games of a doubleheader for Boston over Cleveland, allowing just 10 hits total in the 3–2 and 5–0 victories, which put Boston 2 games ahead of New York in the race.
13th Hoss Radbourn pitches a complete doubleheader for Boston, too, but fails to win either game. After losing the opener to Cleveland, 3–0, he has to hit a HR himself in the 9th inning of the nightcap to salvage a 4–4 tie.
15th Brooklyn increases its lead over St. Louis to 7 games as the Browns lose, 8-1, in Philadelphia while Brooklyn takes a pair from Louisville, 6–5 and 7-2.
Sioux City (Western Association) sweeps a quadruple-header from visiting St. Joseph winning 6–1, 12–7, 12–5, and 5–4 (another researcher lists 6–1, 15–7, 12–5 and 7–4) The first three games are 5 innings apiece and the 4th regularly scheduled game is 7 innings, with two in the morning and two in the afternoon. The scheduling is to allow St. Joes to catch the train to Milwaukee. The next quadrupleheader is September 1903.
16th With Boston losing, 3–2, to the Phillies, the Giants take over first place by a half game with a 12-4 win over the last-place Nationals. Monte Ward leads the way with a grand slam in the 8thoff rookie Alex Ferson, the second off him in a month.
18th The Browns Tommy McCarthy steals 2B, 3B, and home in the 7th inning of a 3–2 St. Louis victory in Kansas City.
19th The New York Giants beat the Phillies, 12-5, to stay a half game ahead of the Beaneaters. Hank O’Day goes to 9-1 for the Giants, after coming over from Washington in a sale on July 26th. He was 2-10 in D.C. O’Day will make it to the Hall of Fame, but as an umpire.
20th Kelly and Nash, each of whom homered earlier in the game, combine hits in the 8th inning to beat Washington, 4–3, and keep the Beaneaters a half game behind the Giants.
21st Four St. Louis errors in the 9th inning give the Reds 4 runs, enabling Cincinnati to win, 5–4.
- Godfrey of the Keene Club while at the bat, is hit on the temple by a ball pitched by James Powers of the Staten Island Athletic Club, and dies several hours later on Staten Island (this is noted in an 1890 New York Clipper article, as pointed out by Peter Morris). In an inquest held on September 24 by Coroner Wood a jury will exonerate Pitcher Powers, the testimony showing that the injury was accidental.
23rd An emergency meeting of the American Association Board of Directors reverses the St. Louis forfeit of September 7th, the game being ruled as a 4–2 Browns victory, although the forfeit of September 8th still stands.
25th The Brotherhood of Professional Base ball Players’ organizational plan for a new Players’ League is leaked to the press in New York. It calls for clubs to be owned jointly by players and capitalists.
26th After Buck Ewing hurts his thumb, Giants sub catcher Willard Brown makes a critical throwing error as New York loses to Chicago, 4–3. New York is now tied with Boston for the NL lead.
27th The Philadelphia NL club releases union activists George Wood and Dan Casey. Meanwhile, the Boston club announces the purchase of the entire WA champion Omaha team for 1890. This latter deal would not actually take place.
28th Jack Stivetts preserves a 2–2 tie for the Browns (AA) by striking out 3 Louisville batters in the 10th inning with a man on 3B.
30th Boston (NL) beats Cleveland 6–3 in 7 innings, while New York ties Pittsburgh 3–3 in 6 innings. This leaves Boston trailing by .002 with a record of 80-43 compared to New York’s 79-42. Each club has 5 games left.