The roots of American baseball and the origins of the rules by which it is played remain elusive. For most of the twentieth century, casual fans were often content to accept as fact the legendary tale that Abner Doubleday had invented baseball in the village of Cooperstown, New York, in 1839. (That tale had romantic appeal because of Doubleday's later service as a Civil War general.) More serious students embraced the alternative version sportswriter Henry Chadwick first advanced in 1860: that baseball derived from rounders, a game Chadwick saw as a youth in England. Late in the twentieth century, well after scholars had discredited the Doubleday myth while leaving Chadwick's explanation intact, new research not only refuted Chadwick's rounders thesis but also presented persuasive evidence about how baseball might have begun and when its rules might first have been set in type.

Rule 1.01 in the Official Baseball Rules defines baseball as “a game between two teams of nine players each, under direction of a manager, played on an enclosed field in accordance with these rules, under jurisdiction of one or more umpires.” Generically, baseball is a stick-and-ball game with the principal offense–defense confrontation matching the batter against the pitcher, who has the statistical advantage. Since baseball’s rules were first codified in the nineteenth century, various rules committees have made adjustments to maintain a suitable competitive balance between offense and defense.