hard knocks vs bad luck

hard knocks and bad luck both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard knocks	Yes	No	No	No
bad luck	Yes	No	No	No

As nouns, bad luck is a hypernym of hard knocks; that is, bad luck is a word with a broader meaning than hard knocks:

Other hypernyms of hard knocks include ill luck, misfortune, tough luck.

hard knocks (noun)	bad luck (noun)
a state of misfortune or affliction	unnecessary and unforeseen trouble resulting from an unfortunate event
	an unpredictable outcome that is unfortunate
	an unfortunate state resulting from unfavorable outcomes