railbird vs sports fan

railbird and sports fan both are nouns.

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

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

railbird: a fan of racing who watches races from the outer rail of the track
sports fan: an enthusiastic devotee of sports

Other hypernyms of railbird include fan, rooter.

railbird (noun)	sports fan (noun)
a fan of racing who watches races from the outer rail of the track	an enthusiastic devotee of sports