He was the ace pitcher on his high school baseball team.
The pitcher stands on the mound.
He served as the pitcher in today's game.
He took the mound as the pitcher in the ninth inning.
The manager changed pitchers in a tight situation.
投手 throws the ball to the batter, while 捕手 is the catcher who receives it—an opposing pair on the same team known as the battery.
投手 is the pitcher, while 野手 refers to any defensive player other than the pitcher (and catcher, depending on context).
打者 is the player who bats, while 投手 is the pitcher who throws to them—the two opposing roles in a baseball at-bat.
投球 refers to the act of pitching or the pitched ball itself, while 投手 refers to the pitcher, the person who throws it.
counter for people
Compound of 投 (throw) and 手 (hand/person), literally 'throwing hand' or 'thrower'.
starting pitcher