The infield is composed of four positions: first base (1B), second base (2B), third base (3B) and shortstop (SS). Generally, the first three have responsibility for plays at their respective bases, although the shortstop often shares responsibility for second base with the second baseman. Each position requires a different set of skills. A player who lacks the offensive or defensive skills needed to be a member of the starting lineup, but who has the various skills needed to play two or more infield positions competently and therefore can be called upon to come off the bench and fill a variety of defensive roles is called a utility infielder.
