Refers specifically to the baseball position behind home plate.
He played catcher on his high school baseball team.
The catcher gets into position after seeing the pitcher's sign.
He played catcher back in high school.
As catcher, he supported the pitcher.
投手 is the pitcher who throws the ball, the position that forms the opposite half of the battery from 捕手, who receives it.
counter for people
Compound of 捕 (catch) and 手 (hand/person), literally 'catching hand' or 'catcher'.