From BR Bullpen
A shutout is a game in which the opposing team does not score a run. A pitcher is credited with a shutout if he pitches a complete game and does not allow a run. The pitcher does not need to win the game to get credit for the shutout, as a shutout is recorded for both teams if a game ends with a score of 0-0 (for example, if it is called because of darkness of rain). Thus, both opposing pitchers may record shutouts during the same game.
When more than one pitcher is used by a team that records a shutout, it is known as a combined shutout. While those are usually listed in the league's season statistics (usually as a separate entry after the alphabetical listing of all pitchers), no statistics are kept as to which pitchers have had a hand in the most combined shutouts in a season or in a career.
With the decrease of complete games in Major League Baseball, shutouts credited to starting pitchers have become relatively rare, and a pitcher can now lead the league with three or four in a season, whereas until the 1980s, there were occasionally pitchers with seasonal shutout totals in the double figures.
 Further Reading
- Warren N. Wilbert: The Shutout in Major League Baseball: A History, McFarland, Jefferson, NC, 2012. ISBN 0786468513