A starting pitcher is credited with a shutout when he pitches the entire game for a team and does not allow the opposition to score. By definition, any pitcher who throws a shutout is also awarded a win. Because he recorded every out for his team and didn't allow a run, his team could only have won.
If a starting pitcher does not allow a run but is removed before the game ends, he is not given credit for a shutout. However, if the ensuing reliever(s) also do not allow a run, the team as a whole is credited with a shutout.
In very rare instances, a pitcher can pitch a shutout if he enters in relief. Per official MLB rule 9.18: "No pitcher shall be credited with pitching a shutout unless he pitches the complete game, or unless he enters the game with none out before the opposing team has scored in the first inning, puts out the side without a run scoring and pitches the rest of the game without allowing a run." The latter represents the only circumstance in which a pitcher is credited with a shutout but not a complete game.
In order to complete a shutout, a pitcher must remain in the game for every out. Even if a pitcher throws nine shutout innings, he is not credited with a shutout if the game goes into extra innings. If a game is shortened by rain, a pitcher is still credited with a shutout if he allows no runs and pitches the entire contest.
Shutouts have become increasingly rare with the growing reliance on bullpens. In order to record one, pitchers generally have to be efficient with their pitches -- as well as physically strong and mentally tough late in games, when fatigue can set in.
Watch: Sonny Gray pitches a shutout.
In A Call
"blanking," "blanked," "held scoreless"