It is common for a pitcher to pitch for several innings and then
be removed in favor of a relief pitcher. Because pitching is
a specialized skill, most pitchers are relatively poor hitters;
it is common to substitute for a pitcher when he is due to bat.
This pinch hitter is typically then replaced by a relief pitcher
when the team returns to the field on defense, but more complicated
substitutions are possible, most notably the double switch.
Many amateur leagues allow a starting player who was removed to
return to the game in the same position in the batting order
under a re-entry rule. Youth leagues often allow free and open
substitution to encourage player participation.
Most leagues, notably Major League Baseball's American League,
allow a designated hitter, a player whose sole purpose is to
hit when it would normally be the pitcher's turn. This is not
considered a substitution but rather a position, albeit a purely
offensive one. A designated hitter does not play in the field
on defense and may remain in the game regardless of changes in