Baseball began with four outfielders and only three infielders to guard the bases.
In 1849, D.L. Adams (1814-1899) realized that three men could cover fly balls in the outfield.
By moving one of these outfield players to the infield he could keep a lot of ground balls from getting through by “stopping them short,” thus giving the new position its name of shortstop.
Technically, the shortstop position is still an outfielder.
