Unexpectedly huge, Robin Hood’s person? (9)
I believe the answer is:
neighbour
'hood's person?' is the definition.
(resident of a neighbourhood)
'unexpectedly huge robin' is the wordplay.
'unexpectedly' is an anagram indicator.
'huge'+'robin'='hugerobin'
'hugerobin' with letters rearranged gives 'NEIGHBOUR'.
(Other definitions for neighbour that I've seen before include "Chap next door" , "Someone in the street" , "Nearby resident" , "Person who lives next door" , "Abut" .)