The 1931 major league baseball season began on April 14, 1931. The regular season ended on September 27, with the St. Louis Cardinals and Philadelphia Athletics as the regular season champions of the National League and American League, respectively. The postseason began with Game 1 of the 28th World Series on October 1 and ended with Game 7 on October 10. In the second iteration of this World Series matchup, the Cardinals defeated the Athletics, four games to three, capturing their second championship in franchise history, since their previous in 1926. Going into the season, the defending World Series champions were the Philadelphia Athletics from the 1930 season.