Understudy with good reputation (8)
I believe the answer is:
standing
'reputation' is the definition.
(one's standing is one's reputation or status)
'understudy with good' is the wordplay.
'understudy' becomes 'standin' (someone who stands in for someone else).
'with' is a charade indicator (letters next to each other).
'good' becomes 'g' (abbreviation).
'standin'+'g'='STANDING'
(Other definitions for standing that I've seen before include "Status, reputation" , "Status - on one's feet" , "Being a candidate - status" , "(Of corn) not yet reaped" , "Bearing" .)