Green’s Dictionary of Slang

one who is constantly beaten up, e.g. an abused woman; also in fig. use.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 45: The squat man [...] made a punching bag of the lanky chap from the start.
1913		Day Book (Chicago) 13 May 1: [headline] Vice and Crime in Chicago About to be Used Again as a Political Punching Bag.
1915		Day Book (Chicago) 13 Nov. 22/1: The wide-awake man is so often made the punching bag for our so-called protector, the chicago officer.
[1937		C. Pifer ‘Executioner’ in All-America Sports Mag. Jan. 🌐 When do we get a chance at your prize pushover after we take care of that old punchin’ bag?].
1955		‘Hal Ellson’ Rock 21: Everybody hits him [...] He’s the punching bag for the whole neighborhood.
1974		(con. 1960s) R. Price Wanderers 76: Scottie had never hit him before, although Scottie was Dougie’s punching bag.
1978		R. Caron Go-Boy! 213: Ulla [...] had just broken up with her gangster friend, Simon, who had used her mostly as a punching bag.
1982		(con. 1970) J. Ehrlichman Witness to Power 99: After all those months as a punching bag, Hickel liked the admiration [...] He was a ‘pop’ hero.
1987		R. Campbell Alice in La-La Land (1999) 44: A whore he picked up from the stroll right out there. A punching bag.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 27: A domestic squawk, the complainant a longtime punching bag.