linebacker vs footballer

linebacker and footballer both are nouns.

Word	Noun	Adjective	Verb	Adverb
linebacker	Yes	No	No	No
footballer	Yes	No	No	No

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

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

Other hypernyms of linebacker include football player.

linebacker (noun)	footballer (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