Work over, drink's knocked back (4)
I believe the answer is:
opus
'work' is the definition.
(an opus is an artistic work)
'over drink's knocked back' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'drink' becomes 'sup' (to sup is to drink).
'knocked back' says the letters should be written backwards.
'sup' in reverse letter order is 'pus'.
'o'+'pus'='OPUS'
(Other definitions for opus that I've seen before include "Musical piece" , "Piece of music (with number)" , "Showing creative skill" , "Composer's work" , "Work or composition, usually musical" .)