sports fan vs enthusiast

sports fan and enthusiast both are nouns.

Word	Noun	Adjective	Verb	Adverb
sports fan	Yes	No	No	No
enthusiast	Yes	No	No	No

As nouns, enthusiast is a hypernym of sports fan; that is, enthusiast is a word with a broader meaning than sports fan:

Other hypernyms of sports fan include partisan, partizan.

sports fan (noun)	enthusiast (noun)
an enthusiastic devotee of sports	an ardent and enthusiastic supporter of some person or activity
	a person having a strong liking for something