victim vs punching bag

victim and punching bag both are nouns.

Word	Noun	Adjective	Verb	Adverb
victim	Yes	No	No	No
punching bag	Yes	No	No	No

As nouns, punching bag is a hyponym of victim; that is, punching bag is a word with a more specific, narrower meaning than victim:

victim (noun)	punching bag (noun)
an unfortunate person who suffers from some adverse circumstance	an inflated ball or bag that is suspended and punched for training in boxing
a person who is tricked or swindled	a person on whom another person vents their anger