MLB history

Baseball's professional structure predates every other major North American league, and much of its current shape — two leagues, a championship series between them — is inherited rather than designed.

The two leagues operated with meaningfully different rules for decades, most visibly over whether pitchers batted. That difference has since been removed, making inter-league play more uniform.

Statistical record-keeping has been part of the sport from the beginning, which is why baseball has the deepest historical numbers of any team sport and why its analytics culture arrived first.