punching bag vs punching ball

punching bag and punching ball both are nouns.

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

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

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

Other synonyms of punching bag include punch bag, punchball.

punching bag (noun)	punching ball (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
a person on whom another person vents their anger