Frenchman is thrown, given an unsuitable role (7)
I believe the answer is:
miscast
'given an unsuitable role' is the definition.
(I've seen this in another clue)
'frenchman is thrown' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur).
'thrown' becomes 'cast' (I've seen this before).
'm'+'is'+'cast'='MISCAST'
(Other definitions for miscast that I've seen before include "Of actor, assigned to unsuitable role" , "Give an unsuitable role" , "Of actor, unsuited to a role" , "part poorly chosen" , "Given an unsuitable part" .)