Rule Differences Between MLB's American and National Leagues

Spring training and Opening Day bring new and casual fans, and a common question is whether the American and National Leagues play by different rules. Major League Baseball is organized into two leagues that grew separately in the sport's early days. By the end of the 19th century the American League and the older National League were the clear giants and agreed to share the spotlight and the World Series, yet for much of their history they operated largely independently, with the American League known for scoring and the National League more of a pitcher’s playground.

They legally merged into the modern MLB at the end of the 20th century, and that change brought more interleague play, greater player movement between leagues, and rule standardization across both leagues. The last major rule difference was the designated hitter: the American League adopted it in the 1970s while the National League resisted, and the universal designated hitter was standardized across both leagues in 2022.

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