January 30 – The Cincinnati Reds hire Pat Moran as manager when no word is received from manager Christy Mathewson, who is still in France.
January 31 – Future Hall of Fame member Jackie Robinson is born to Jerry and Mallie Robinson in Cairo, Georgia. Robinson will become the first African American player in 20th century major league history when he debuts for the Brooklyn Dodgers in 1947.
February 1 – After winning an out-of-court settlement of his suit against the Brooklyn Robins for the balance of his salary ($2,150) when the 1918 season ended a month early, former MVP Jake Daubert is traded to the Reds for OF Tommy Griffith.
February 5 – Charges brought in 1918 by Reds owner Garry Herrmann and manager Christy Mathewson against Hal Chase for betting against his team and throwing games in collusion with gamblers are dismissed by National League president John Heydler.
February 21 – The New York Yankees acquire 45-year-old spitballer Jack Quinn from Vernon (PCL), sending in exchange P Happy Finneran, 1B Zinn Beck, and cash. Quinn will be named a designated spitballer when the wet pitch is outlawed, and in 1921 he will help the Yankees to their first American League pennant. Quinn won't call it quits until he's 50.
March 1 – Philadelphia Athletics owner Connie Mack makes one of his biggest player mistakes, trading 3B Larry Gardner, OF Charlie Jamieson, and P Elmer Myers to Cleveland in exchange for OF Braggo Roth. Vet writer Ernest Lanigan predicts that Roth will lead the circuit in homers at Shibe Park, but Roth will be shipped on to Boston by midseason. Gardner will put in six more .300 years, and Jamieson will be a top leadoff man and .303 hitter for the next 14 years.
May 4 – The New York Giants play their first legal Sunday game at home, before 35,000 fans, losing to the Philadelphia Phillies, 4–3. More than 25,000 turn out in Brooklyn the same day. By early June, the Giants will outdraw their 1918 attendance.
Cincinnati Reds right-hander Hod Eller pitches a 6–0 no-hitter over the St. Louis Cardinals.
Walter Johnson retires 28 consecutive batters during a 12-inning scoreless tie against Jack Quinn and the New York Yankees. Future football immortal George Halas, batting leadoff for New York, goes 0-for-5 with two strikeouts.
May 15 – The Cincinnati Reds bomb Al Mamaux for 10 runs in the 13th innings to beat the Brooklyn Robins, 10–0. Reds RF Greassy Neale has a record 10 putouts.
May 20 – Red Sox pitcher babe Ruth hit his first career grand slam home run; the bomb comes against Dave Davenport of the St. Louis Browns in St. Louis. Boston wins 6–4.
May 21 – The Giants send Jim Thorpe to Boston for the $1,500 waiver price.
May 23 – It's Hank Gowdy Day in Boston, the catcher's first game after returning from the Army. He hits the first pitch he sees for a single.
July 1 – Going 5-for-5 in a 9–4 win over the Phillies, Brooklyn's Ed Konetchy gets his 10th straight hit, tying Jake Gettman's record set with Washington in 1897. Both will be topped by Walt Dropo in 1952.
July 6 – William Veeck, former sportswriter, replaces Fred Mitchell as Chicago Cubs president, but Mitchell remains as manager for the team.
August 8 – The Pittsburgh Pirates trades Casey Stengel to the Phillies for Possum Whitted, who will bat .389 for Pittsburgh in the last 35 games of the season.
August 11 – Cleveland's Tris Speaker ties an AL record, scoring five runs in a 15–9 win at New York.
Babe Ruth hits his 17th home run, the first of seven homers in 12 days, which will include his fourth grand slam, setting an AL record until 1959. The Yankees overcome Muddy Ruel's hitting into a triple play and beat the Tigers in 15 innings, 5–4.
Chicago White Sox CF Happy Felsch ties the major-league record with four OF assists in one game, but the Boston Red Sox beats Chicago 15–6.
The Brooklyn Robins waste no time in splitting a pair with the Chicago Cubs, losing 2–0 in an hour and 10 minutes, then winning 1–0 in one hour and seven minutes in the second game.
August 16 – The St. Louis Browns set an AL record with 53 total chances against the Philadelphia Athletics, but lose 7–4. The Browns have 26 assists and St. Louis 1B George Sisler has 17 putouts. With no putouts, the St. Louis outfielders have the day off.
August 20 – Wichita OF Joe Wilhoit (Western League) fails to get a hit, ending a 69-game streak in which he collected 155 hits in 299 at bats for a .505 batting average. The previous record was 49 by Oakland's Jack Ness (Pacific Coast League) in 1915.
August 24 – Cleveland Indians P Ray Caldwell is flattened by a bolt of lightning in his debut with the team. He recovers to get the final out of the game, and defeats the Philadelphia Athletics 2–1.
August 26 – New York Giants 1B Hal Chase handles 35 chances against the Pittsburgh Pirates during a doubleheader.
September 10 – Cleveland Indians' pitcher Ray Caldwell, struck by lightning 2 weeks earlier, no-hits his former teammates New York Yankees 3–0 at the Polo Grounds.
September 16 – Dutch Ruether beats the New York Giants, 4–3, to clinch the Cincinnati Reds first pennant since their American Association days.
September 20 – Babe Ruth ties Ned Williamson's major-league home run mark of 27 with a game-winner off Lefty Williams of the Chicago White Sox. Four days later, Ruth will hit his 28 over the roof of the Polo Grounds.
September 21 – The Cubs beat the Braves 3–0 in 58 minutes of playing time. It takes the Robins 55 minutes to beat the Reds 3–1. Slim Sallee throws 65 pitches, topping Christy Mathewson's 69-pitch complete game. One week later the Giants will close the season beating the Phillies, 6–1, to set a record 51 minutes.
The Chicago White Sox' 6–5 win over the St. Louis Browns clinches the AL pennant; the final margin will be 3½ games over the Cleveland Indians.
The Brooklyn Robins defeat the Phillies twice on Fred Luderus Day in Philadelphia. The second game is the 528th in a row played by the Phillies 1B, who is presented with a diamond stickpin and gold watch between games to commemorate his endurance effort. He will end the season with a consecutive-game streak of 533.
Boston Red Sox pitcher Waite Hoyt throws nine perfect innings against the New York Yankees, but they come in the 13th in which he gives up hits to lose 2–1.
September 27 – Babe Ruth hit his 29th home run and his first of the year in Washington, to become the first player to hit at least one home run in every AL park in the same season.
September 28 – On the last day of the season, Jesse Barnes won his National League-leading 25th victory, 6–1, over Lee Meadows and the Philadelphia Phillies at Polo Grounds. The game was played at a feverish pace and lasted a mere 51 minutes, a major league record that still stands as the shortest nine-inning game ever played.
November 10 – Clark Griffith becomes a club owner and president when he joins Philadelphia grain broker William Richardson in buying controlling interest in the Washington Senators for $175,000. Griffith, unable to get financial help from the American League, mortgages his Montana ranch to raise funds.
The National League votes to ban the spitball's use by all new pitchers. The ban will be formally worked out by the Rules Committee in February.
With the opposition led by New York, Boston, and Chicago owners, the American League directors pass a resolution accusing Ban Johnson of overstepping his duties. They demand that league files be turned over to them and that an auditor review all financial accounts.
December 26 – Although it will not be officially announced until January, the New York Yankees buy Babe Ruth from financially pressed Harry Frazee, paying $125,000 (one-fourth cash, plus $25,000 a year at six percent) plus guaranteeing a $300,000 loan with Fenway Park as collateral.
January 1 – Gene Curtis, 35, outfielder for the 1903 Pittsburgh Pirates.
January 3 – Al Schellhase, 54, outfielder for the 1890 Boston Beaneaters (NL) and the 1891 Louisville Colonels (AA).
January 3 – Art Rico, 23, Italian-born catcher who played from 1916 through 1917 for the Boston Braves of the National League.
January 6 – Jake Stenzel, 51, National League center fielder for four different clubs between 1890 and 1899, a five-time .300 hitter whose career batting average of .339 is the 12th highest in Major League history.
January 8 – Jim O'Rourke, 68, left fielder for Boston, Buffalo and New York who batted .314 lifetime and ended his career ranked second all-time in games, hits, runs, doubles and total bases; made first hit in major league history after four seasons in National Association, and later became oldest player ever to get a hit at age 54; led NL in hits, runs, home runs, triples and walks once each; later a minor league manager and executive.
January 23 – John Newell, 51, third baseman who played for the Pittsburgh Pirates during the 1891 season.
February 7 – Lefty Davis, 44, outfielder who hit .261 in 348 games with the Pirates, Highlanders, Reds and Superbas between 1901 and 1907.