Person who stands up for fullback? (8)

I believe the answer is:

defender

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'person' is the definition.
(defender is a kind of person)

I can't explain the rest of the clue.

(Other definitions for defender that I've seen before include "One on team" , "One who protects from danger or takes one's side" , "One who protects others" , "one aiming to retain his title" , "supporter" .)

I've seen this clue in The Daily Express.

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