Resistance of French fellow who's engaged (8)
I believe the answer is:
defiance
'resistance' is the definition.
(defiance is a kind of resistance)
'of french fellow who's engaged' is the wordplay.
'of french' becomes 'de' ('of' in French).
'fellow who's engaged' becomes 'fiance' (a man engaged to be married).
'de'+'fiance'='DEFIANCE'
(Other definitions for defiance that I've seen before include "Challenging behaviour" , "bold opposition" , "show of rebellion" , "Insubordination" , "Hostile challenge" .)