February 27 – The sacrifice fly rule is adopted. No time at bat is charged if a run scores after the catch of a fly ball. The rule will be repealed in 1931, then reinstated several times before gaining permanent acceptance in.
September 23 – The Chicago Cubs and New York Giants, involved in a tight pennant race, were tied in the bottom of the ninth inning at the Polo Grounds. The Giants had runners on first and third and two outs when Al Bridwell hit a single to center field, scoring Moose McCormick from third with the Giants’ apparent winning run, but the runner on first base, rookie Fred Merkle, thinking the game was over, went half way to second and then sprinted to the clubhouse after McCormick touched home plate. As fans swarmed the field, Cub infielder Johnny Evers retrieved the ball and touched second. A forceout was called at second base, nullifying the single, and since there were 2 outs when the play started, the run was also nullified and the inning ended. The game was declared a tie and would be made up at the end of the season if the Cubs and Giants were tied for first place. The incident became known as "Merkle's Boner".
September 26 – Ed Reulbach of the Chicago Cubs pitches two shutouts in the same day, whitewashing the Brooklyn Superbas 5–0 on a five-hitter and 3–0 on a three-hitter. The entire doubleheader is played in less than three hours. Reulbach allows five hits in the a.m. game, and is even stingier in the afternoon, yielding three hits and a walk. Kaiser Wilhelm and Jim Pastorius are the losing pitchers.
October–December
October 2
*In a game involving the Cleveland Naps and the Chicago White Sox, Ed Walshstruck out 15 Naps and walked one batter, pitching a complete game, but it was not enough as Addie Joss pitched a perfect game, as the Naps beat the White Sox, 1-0, during the heat of a pennant race. Cleveland center fielder Joe Birmingham scored the game's only run. Joss' perfect game is the second in the modern era and fourth all time. It is perhaps the finest pitching duel in baseball history.
*Washington Senators outfielder Otis Clymerhits for the cycle in a 12-2 Washington victory over the New York Highlanders.
October 6 – The Detroit Tigers defeat the Chicago White Sox, 7-0, to win the American League pennant on the last day of the season.
October 8 – The Chicago Cubs defeat the New York Giants, 4-2, in the make-up of "The Merkle's Boner" game, giving the Cubs the National League pennant.
October 14 – The Chicago Cubs defeat the Detroit Tigers, 2-0, in Game 5 of the World Series to win the series four games to one. It is the second consecutive World Championship for the Cubs and the second year in a row they have defeated the Tigers in the World Series. The Cubs did not win another World Series until 2016, when they defeated Cleveland Indians in seven games, this ended its 108 year championship drought.
October 14 – The baseball season of 1908 ends with the lowest runs per game average in major league baseball history at 3.38. This outcome was likely an important factor in the decision to trial a livelier "cork center" ball in both leagues the following season.
October 24 – "Take Me Out to the Ball Game" is introduced by singer Billy Murray. The songwriting team of Albert Von Tilzer and Jack Norworth who created the immortal tune have never seen a game. Over the past 100 years, more than 400 musicians from every conceivable genre have recorded the song.
November 22 – In the first game ever between a Japanese and an American professional team, the Reach All-Americans defeat Waseda University in Tokyo, 5 – 0.
April 6 – Jim Brown, 47, pitcher and outfielder for two seasons, 1884 and 1886.
April 10 – Mike Griffin, 43, center fielder for Baltimore and Brooklyn who batted.300 six times, scored 100 runs ten times; led league in runs and doubles once each.
April 13 – John Kelly, 49, 19th century catcher, manager and umpire.
April 20 – Henry Chadwick, 83, the "Father of Baseball", who through his writings, analysis of statistics and service in developing the sport's rules played a principal role in establishing baseball as the "national pastime"; devised the box score, developed scoring system which enabled recording of every play, authored the first rule book in 1858, and created statistics including batting average and earned run average; worked to revise sport's rules so as to balance offense and defense, and to increase mental demands as well as physical ones.
May–August
May 9 – Charlie Nyce, 37, shortstop for the 1895 Boston Beaneaters.
May 14 – John O'Connell, 35, played in only the 1891 and 1902 season.
May 24 – Pete Hasney, for the 1890 Philadelphia Athletics of the American Association.
June 16 – Ned Garvin, 34, pitcher who posted a 57-97 record and a 2.72 ERA for five different teams between 1896 and 1904.
June 22 – Everett Mills, 63, first baseman for six seasons, 1871–1876.
July 18 – John Brown, 31, pitcher for the 1897 Brooklyn Bridegrooms.
July 22 – Pete Sommers, 41, catcher who played with six clubs from 1897 to 1890.
August 19 – Doc Bushong, 51, catcher for 13 seasons, who played on five league championship teams.
August 20 – Marty Honan, 39, catcher for the 1891 Chicago Colts of the National League.
August 24 – George Meister, 44, German third baseman who hit.194 in 34 games for the 1884 Toledo Blue Stockings.
September–December
September 7 – Bill Morgan, 52, outfielder and shortstop who played with the Pittsburgh Alleghenys and Washington Nationals.
September 14 – Ike Van Zandt, 32, outfielder and pitcher who played for the New York Giants, Chicago Cubs and St. Louis Browns.
September 18 – Dickey Pearce, 72, shortstop whose career spanned the years 1856 to 1877; introduced the bunt and pioneered defensive play at his position, later became an umpire.
September 28 – Tom Pratt, 64, played at first base for one game with the 1871 Philadelphia Athletics.
November 5 – Pat Hannivan, 42, outfielder and second baseman for the 1897 Brooklyn Bridegrooms.
December 8 – Frank Griffith, 36, pitcher for the Chicago Cubs and Cleveland Spiders.
December 10 – Wild Bill Widner, 41, pitcher who posted a 22-36 record and a 4.36 ERA with the Red Stockings, Nationals, Solons and Kelly's Killers from 1887 to 1891.
December 19 – Reddy Foster, 44, pinch hitter for the 1896 New York Giants.
December 26 – Charlie Householder, 52, third baseman/left fielder/shortstop who hit.239 in 83 games for the 1884 Chicago/Pittsburgh team of the Union Association.
December 26 – Shadow Pyle, 47, pitcher for the Philadelphia Quakers and Chicago White Stockings.
