Nobleman before Duke is opposed (9)
I believe the answer is:
countered
'is opposed' is the definition.
(to counter is to hit back or oppose)
'nobleman before duke' is the wordplay.
'nobleman' becomes 'count' (count is a kind of nobleman).
'before' becomes 'ere' (poetic term).
'duke' becomes 'd' (abbreviation).
'count'+'ere'+'d'='COUNTERED'
(Other definitions for countered that I've seen before include "Opposed" , "Answered a chess move" , "returned" , "Contradicted" .)