left-handed pitcher
Baseball term for a pitcher who throws with the left hand.
チームには左投手が二人いる。
The team has two left-handed pitchers.
右投手 is a right-handed pitcher, the opposite of 左投手.
左腕 can also refer to a left-handed pitcher in baseball contexts, but more broadly means 'left arm'.
Compound of 左 (ひだり, 'left') and 投手 (とうしゅ, 'pitcher').