punching ball vs punch bag

punching ball and punch bag both are nouns.

Word	Noun	Adjective	Verb	Adverb
punching ball	Yes	No	No	No
punch bag	Yes	No	No	No

As nouns, punching ball and punch bag are synonyms defined as:

punching ball and punch bag: an inflated ball or bag that is suspended and punched for training in boxing

Other synonyms of punching ball include punchball, punching bag.

punching ball (noun)	punch bag (noun)
an inflated ball or bag that is suspended and punched for training in boxing	an inflated ball or bag that is suspended and punched for training in boxing