Frenchman unusually enraged about a policeman (8)
I believe the answer is:
gendarme
'a policeman' is the definition.
(I know that gendarme is a type of policeman)
'frenchman unusually enraged about' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'unusually' indicates anagramming the letters.
'about' is an insertion indicator.
'enraged' is an anagram of 'gendare'.
'm' inserted inside 'gendare' is 'GENDARME'.
(Other definitions for gendarme that I've seen before include "Law enforcer" , "continental copper" , "French copper" , "Force man" , "policeman in Paris?" .)