Grounds to accept setter's judgement (8)
I believe the answer is:
estimate
'judgement' is the definition.
(estimate is a kind of judgement)
'grounds to accept setter's' is the wordplay.
'grounds' becomes 'estate' (I've seen this before**).
'to accept' indicates putting letters inside.
'setter's' becomes 'im' (I've seen this in other clues).
'estate' enclosing 'im' is 'ESTIMATE'.
(Other definitions for estimate that I've seen before include "Calculate - valuation" , "Evaluate - approximation" , "Calculate roughly" , "Reckon value" , "Calculate approximately" .)