linebacker vs football player

linebacker and football player both are nouns.

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

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

linebacker: a defensive football player who takes a position close behind the linemen
football player: an athlete who plays American football

Other hypernyms of linebacker include footballer.

linebacker (noun)	football player (noun)
(American football) the position of a defensive football player who plays close behind the line of scrimmage	an athlete who plays American football
a defensive football player who takes a position close behind the linemen