(Spor) A punching bag (US) or punch-bag (UK) is a sturdy bag designed to be repeatedly punched, for use in physical exercise or stress relief in order to improve one of three areas: physical strength, aerobic fitness, or punching technique
an inflated ball or bag that is suspended and punched for training in boxing a person on whom another person vents their anger; "he resigned because his boss used him as a punching bag