Agitated nervous response by loud Frenchman (8)
I believe the answer is:
frenetic
'agitated' is the definition.
('frenetic' can be similar in meaning to 'agitated')
'nervous response by loud frenchman' is the wordplay.
'nervous response' becomes 'tic' (I've seen this before).
'by' means one lot of letters go next to another.
'loud' becomes 'f' (A musical term).
'frenchman' becomes 'rene'.
'f'+'rene'='frene'
'tic' put after 'frene' is 'FRENETIC'.
(Other definitions for frenetic that I've seen before include "Lively" , "Mad" , "Demented" , "Maniacal" , "Hectic" .)