Against work, sat (7)
I believe the answer is:
opposed
'against' is the definition.
(I've seen this before)
'work sat' is the wordplay.
'work' becomes 'op' (short for opus).
'sat' becomes 'posed' ('pose' can be a synonym of 'sit').
'op'+'posed'='OPPOSED'
(Other definitions for opposed that I've seen before include "Fought back" , "Withstood" , "Objected to" , "Confronted" , "Stood against" .)