Noblemen harm wine (9)
'noblemen' is the definition.
(margrave is a kind of nobleman)
'harm wine' is the wordplay.
'harm' becomes 'mar' (I've seen this before).
'wine' becomes 'graves' (left bank subregion of Bordeaux in France).
(Other definitions for margraves that I've seen before include "aristocrats abroad", "Noblemen".)