hard knocks vs disaster

hard knocks and disaster both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard knocks	Yes	No	No	No
disaster	Yes	No	No	No

As nouns, disaster is a hyponym of hard knocks; that is, disaster is a word with a more specific, narrower meaning than hard knocks:

Other hyponyms of hard knocks include ill-being, catastrophe, extremity, distress, affliction, victimization, low-water mark, nadir.

hard knocks (noun)	disaster (noun)
a state of misfortune or affliction	an act that has disastrous consequences
	an event resulting in great loss and misfortune
	a state of extreme (usually irremediable) ruin and misfortune