Ref eating pork pie in break (6)
I believe the answer is:
'break' is the definition.
(relief is a kind of break)
'ref eating pork pie' is the wordplay.
'eating' indicates putting letters inside.
'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 "Person replacing another on duty" , "Easement from pain or stress" , "- - of Mafeking" , "Removal of a burden" , "It means less stress" .)