Exploited worker knocking back some refreshments (4)
I believe the answer is:
serf
'exploited worker' is the definition.
(worker in feudal times)
'knocking back some refreshments' is the wordplay.
'knocking back' shows that the letters should be reversed in order.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'fres' is hidden within 'refreshments'.
'fres' written backwards gives 'SERF'.
(Other definitions for serf that I've seen before include "Tied estate worker" , "Worker bound" , "Servant, vassal" , "Peasant, agricultural labourer" , "labourer with no property of his own" .)