April 15 – The American League season opened with Boston Red Sox ace Babe Ruth pitching a four-hit, 7–1 victory over the Philadelphia Athletics. Shortly after, Boston manager Ed Barrow started Ruth's conversion to slugger by working him into seventy-two games as an outfielder–first baseman.
April 18 – Cleveland Indians center fielderTris Speaker turned an unassisted double play against the Detroit Tigers. Eleven days later, Speaker duplicated the feat against the Chicago White Sox for the fourth unassisted double play of his career to set a franchise record that he would later share with teammate Elmer Smith.
May 14 – Sunday baseball was officially legalized in Washington, D.C. after district commissioners finally rescinded the ban in response to the large increase in the city's wartime population and the need for more recreational activities.
June 3 – Dutch Leonard tosses the second no-hitter of his career, leading the Boston Red Sox to a 5–0 victory over the Detroit Tigers.
August 1 – The Pittsburgh Pirates and the Boston Braves went head-to-head for a major-league record twenty scoreless innings. Marathon man Art Nehf went the distance for Boston, but was eventually beaten 2–0 in the twenty-first inning.
August 9 – Cincinnati Reds manager Christy Mathewson suspended Hal Chase indefinitely after suspecting him of taking bribes to fix games. Chase was eventually reinstated and returned to play for the New York Giants in 1919.
September 1 – During the regular season, Washington Senators ace Walter Johnson completed fifteen extra inning games, including two of eighteen innings, one of sixteen innings, and another of fifteen innings.
September 5 – During the 7th inning stretch in Game 1 of the World Series, a military band played the Star Spangled Banner as a tribute to all servicemen on leave and in attendance. From then on, the song was played at every World Series outing and every season opener, though it was not yet adopted as the national anthem. The custom of playing it before every game began during World War II, after the installation of stadium speaker systems made it more feasible.
September 11 – Against the backdrop of World War I, which forced the premature ending to the regular season on September 1, the Boston Red Sox defeated the Chicago Cubs, 2–1, in Game 6 of the World Series to win their fifth world championship, and third in four years, four games to two. The Red Sox would not win another championship for the next 86 years.
March 2 – George Kaiserling, 24, pitcher who played from 1914 through 1915 with the Indianapolis Hoosiers and the Newark Pepper of the Federal League.
March 4 – Lon Ury, 40, first baseman for the 1903 St. Louis Cardinals.
March 10 – Jim McCormick, 61, pitcher who posted a 265–214 record with a 2.43 ERA for six different teams between 1878 and 1897, who is regarded as the first ballplayer born in Glasgow to appear in a major league game.
March 22 – Jim Holdsworth, 67, shortstop for seven different teams in a nine season career that spanned between 1870 and 1884.
March 24 – Jack Farrell, 25, second baseman who played from 1914 to 1915 for the Chicago Whales.
April 6 – Bill Bowman, 49, catcher for the 1891 Chicago Colts.
April 6 – Newt Halliday, 21, first baseman for the 1916 Pittsburgh Pirates.
April 9 – Ed Wilkinson, 27, outfielder and infielder for the 1912 New York Highlanders of the American League.
April 10 – Owen Shannon, 38, backup catcher for the 1907 Washington Senators of the American League.
May 26 – George Bone, 43, shortstop for the 1901 Milwaukee Brewers of the American League.
June 11 – Mike Hickey, 46, second baseman who appeared in one game for the 1899 Boston Beaneaters of the National League.
June 12 – Larry Ressler, 69, outfielder who played during the 1875 season for the Washington Nationals of the National Association, who is recognized as the first player born in France to play in American professional baseball.
June 14 – George Wheeler, 36, pinch hitter who played in three games for the Cincinnati Reds in the 1910 season.
June 21 – Davy Force, 68, shortstop who posted a .249 average with 1060 hits and 653 runs scored in 1029 games for nine different teams between 1871 and 1886.
June 25 – Jake Beckley, 50, owner of the major league record for career games as a first baseman, a .308 career hitter who retired with the second most hits in major league history.
November 7 – Mike Tiernan, 51, right fielder who played exclusively for the New York Giants from 1887 through 1899, compiling a .311 average with 106 home runs, 853 RBI, 1316 runs and 428 stolen bases in 1478 games.
November 8 – Larry Chappell, 28, outfielder for the Chicago White Sox, Cleveland Indians and Boston Braves from 1913 to 1917, who died in an army camp from the Spanish flu pandemic while serving in World War I.
December 4 – Walt Dickson, 40, who pitched from 1910 through 1915 for the Boston Braves, Pittsburgh Rebels and New York Giants.
December 8 – Ed Mincher, 67, National Association outfielder who played from 1868 to 1872 for the Baltimore Marylands, Fort Wayne Kekiongas and Washington Nationals.
December 10 – Lester Dole, 63, outfielder for the 1875 New Haven Elm Citys of the National Association.
December 13 – Frank Arellanes, 36, Mexican-American pitcher for the Boston Red Sox from 1908 to 1910, who died in San Jose, California, victim of the Spanish flu pandemic.
December 20 – Silk O'Loughlin, 48, American League umpire since 1902 who worked in a record ten no-hitters and introduced the practice of shouting calls for balls, strikes and outs.
December 25 – Bob Blakiston, 63, outfielder who played from 1882 to 1884 in the American Association for the Philadelphia Athletics and Indianapolis Hoosiers.