Official eats pork pie in break (6)
I believe the answer is:
'break' is the definition.
(I know that relief is a type of break)
'official eats pork pie' is the wordplay.
'official' becomes 'ref' (match official in football, say).
'eats' means one lot of letters goes inside another.
'pork pie' becomes 'lie' ('pork pie' is Cockney rhyming slang for a lie).
'ref' placed around 'lie' is 'RELIEF'.
'in' is the link.
(Other definitions for relief that I've seen before include "That's a load off my mind" , "Break" , "Relaxation following distress" , "Freeing of besieged city" , "A lessening of pressure" .)