line backer vs footballer

line backer and footballer both are nouns.

Word	Noun	Adjective	Verb	Adverb
line backer	Yes	No	No	No
footballer	Yes	No	No	No

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

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

Other hypernyms of line backer include football player.

line backer (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