1931 Major League Baseball season

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 a rematch of the prior year's postseason, the Cardinals defeated the Athletics, four games to three.

This was the first season that the Baseball Writers' Association of America (BBWAA) selected a Most Valuable Player in each league.

Schedule
The 1931 schedule consisted of 154 games for all teams in the American League and National League, each of which had eight teams. Each team was scheduled to play 22 games against the other seven teams of their respective league. This continued the format put in place since the season (except for ) and would be used until  in the American League and  in the National League.

Opening Day, April 14, featured all sixteen teams, the first time since the season. The final day of the regular season was on September 27, which also saw all sixteen teams play on the final day continuing the trend which began the previous season. This was the first time that both Opening Day and the final day of the season saw all sixteen teams play. The World Series took place between October 1 and October 10.

Rule changes
The 1931 season saw the following rule changes:
 * The National League implements the ground rule double rule, which states that balls that bounce over the fence entitle the batter to two bases. The rule was previously implemented by the American League in.
 * The American League adopted the early- rule that when calling home runs, balls are to be called based on where the ball crosses the outfield fence, no matter if the ball lands in the stands or leaves the ballpark. The National League previously implemented this rule in.
 * The rule previously implemented in, that a sacrifice hit was awarded when any base runner advanced on a fly out, was eliminated.
 * Regulations referring to a batter contacting his own ball were clarified as was the area of bases awarded a batter when a defensive player threw his glove at a batted or thrown ball or in the case of spectator interference.

Bracket
 

American League
1 American League Triple Crown pitching winner

Awards and honors

 * MLB Most Valuable Player Award
 * Lefty Grove, Philadelphia Athletics, P
 * Frankie Frisch, St. Louis Cardinals, 2B

Events

 * July 12 – the Chicago Cubs—St. Louis doubleheader has 33 doubles. Due to the large crowd spilling onto the field, any ball hit into them is a ground-rule double.
 * August 29 – Facing Cincinnati Reds pitcher Si Johnson in his second at bat in the major leagues, Chicago Cubs player Billy Herman hits Johnson's pitch, which ricochets off the bat and hits Herman in the head, knocking him out.