From BR Bullpen
A relief pitcher (aka reliever, collectively the bullpen) is a pitcher who specializes is coming into a game started by another pitcher. The difference in usage patterns goes beyond when the pitchers are brought into the game. Unlike starters, who are given several days off after each appearance, relievers are expected to be able to pitch in several consecutive games.
A relatively recent development in relief pitching is the use of relievers in highly specific roles. Rather than using all relievers in essentially the same way, as teams do with their starters, managers now try to use each reliever in one of a small number of stereotypical roles that depend on the game situation and opposing batter. The most common roles include:
- Long relievers are brought into the game when the starting pitcher is pulled from the game early because of injury or ineffectiveness. The long reliever is expected to pitch until the point of the game where a starting pitcher normally would have been pulled, typically several innings. A long reliever who is used only in lost causes is called a mop-up man.
- Middle relievers are used later in the game than long relievers, typically in the 6th or 7th inning, and used for about one inning. Middle relievers are often brought into the middle of an inning when the starter has let several batters reach base. They may also be used in the late innings of games which their team is losing.
- LOOGYs are Lefty One Out GuYs, left handed relievers who are used to get one or two critical outs against the opponents' best left handed hitters. LOOGYs are almost always used with runners on base.
- Setup men are brought into the game in the 7th or 8th inning to bridge the gap between the starter or middle reliever and the closer. Setup men are normally reserved for close games.
- Closers are used to "close out" games that their team is winning. Most managers will reserve their closer for save situations, i.e. starting the 9th inning with a 1-3 run lead.
 Further Reading
- Fran Zimniuch: Fireman: The Evolution of the Closer in Baseball, Triumph Books, Chicago, IL, 2010.
 Related Sites
- 2004 Article on Closers in The Hardball Times
- Article on LOOGYs in The Hardball Times, part 1
- Article on LOOGYs in The Hardball Times, part 2
- 2005 Article on Closers in The Hardball Times, part 1
- 2005 Article on Closers in The Hardball Times, part 2
- Article on the comparative difficulty of relief pitching versus starting in The Hardball Times