Insider from Acton wrongly claiming prize (8)
I believe the answer is:
occupant
'insider' is the definition.
(I've seen this before)
'acton wrongly claiming prize' is the wordplay.
'wrongly' indicates an anagram.
'claiming' means one lot of letters goes inside another.
'prize' becomes 'cup' (cup is a kind of prize).
'acton' with letters rearranged gives 'ocant'.
'ocant' placed around 'cup' is 'OCCUPANT'.
'from' acts as a link.
(Other definitions for occupant that I've seen before include "Indweller" , "Homeowner or tenant" , "Inmate" , "Inhabitant, resident" , "One in residence" .)