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starting pitcher

n. 1 (context baseball English) A pitcher who is usually used to start a game; a member of a team's rotation. Compare relief pitcher. 2 (context baseball English) A pitcher who is recorded to begin the game.

WordNet
starting pitcher

n. (baseball) a pitcher who starts in a baseball game

Wikipedia
Starting pitcher

In baseball ( hardball or softball), a starting pitcher or starter is the first pitcher in the game for each team. A pitcher is credited with a game started if they throw the first pitch to the opponent's first batter of a game. A pitcher who enters the game after the first pitch of the game is a relief pitcher. Starting pitchers are expected to pitch for a significant portion of the game, although their ability to do this depends on many factors, including effectiveness, stamina, health, and strategy.

A starting pitcher in professional baseball usually rests three, four, or five days after pitching a game before pitching another. Therefore, most professional baseball teams have four, five or six starting pitchers on their rosters. These pitchers, and the sequence in which they pitch, is known as the rotation. In modern baseball, a five-man rotation is most common.