footballer vs blocker

footballer and blocker both are nouns.

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

As nouns, blocker is a hyponym of footballer; that is, blocker is a word with a more specific, narrower meaning than footballer:

footballer: an athlete who plays American football
blocker: a football player whose responsibility is to block players attempting to stop an offensive play

footballer (noun)	blocker (noun)
an athlete who plays American football	a class of drugs that inhibit (block) some biological process
	a football player whose responsibility is to block players attempting to stop an offensive play