football player vs athlete

football player and athlete both are nouns.

Word	Noun	Adjective	Verb	Adverb
football player	Yes	No	No	No
athlete	Yes	No	No	No

As nouns, athlete is a hypernym of football player; that is, athlete is a word with a broader meaning than football player:

Other hypernyms of football player include jock, participant, player.

football player (noun)	athlete (noun)
an athlete who plays American football	a person trained to compete in sports