Attack the little devil with a broken gun (6)
I believe the answer is:
impugn
'attack' is the definition.
(I've seen this before)
'the little devil with a broken gun' is the wordplay.
'the little devil' becomes 'imp' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'a broken' indicates anagramming the letters.
'gun' with letters rearranged gives 'ugn'.
'imp'+'ugn'='IMPUGN'
(Other definitions for impugn that I've seen before include "Attack as false, challenge" , "Challenge (e.g. honesty)" , "Call into question; criticise" , "Blacken the name of" , "Nip mug badly and call in question" .)