When contracts for athletes began growing and players became commodities in the sports business, baseball coaches sought to find ways to preserve their pitchers’ arms and prevent injury. Decades ago, pitchers would start the game and pitch until the game was over, or close to it. Today, starting pitchers rarely throw complete games and are replaced after several innings – depending on the starting pitcher’s performance – by a relief pitcher. The relief pitcher comes into the middle or end of the game with a fresh arm, ready to throw as many pitches as necessary. This not only preserves the starting pitcher’s arm, but it also serves as a strategic move, putting a fresh pitcher in against a batter or playing the odds of a right- or left-handed relief pitcher against a certain batter who might hit poorly against one or the other.

There are generally two types of relief pitcher: the middle reliever and the closer. The middle relief pitcher comes into the game after the starting pitcher has reached a certain pitch count or performs poorly during the first few innings. The middle relief pitcher enters the game any time between the second and eighth innings, but more typically between the sixth and eighth inning. His job is to pitch long enough and well enough to sustain the team until the eighth or ninth inning, at which point the closer comes in.

The closing relief pitcher is trained to end the game. He comes in around the eighth or ninth inning, but more typically the ninth inning. His sole responsibility is to keep opposing batters from effectively reaching base and scoring runs. The closer provides yet another fresh arm late in the game when most batters are tired and their swings slower.

While neither the middle relief pitcher nor the closing relief pitcher typically throw as many pitches as the starting pitcher, it is possible that either one could enter a game and throw for several innings. But because the relief pitcher generally throws fewer pitches than a starting pitcher and stays in the game for less time, their arms tend to stay strong for many years, allowing for longer careers. Both types of relief pitcher play an important role in winning baseball games and open up strategic moves for managers looking to give his team an edge.