Knocks out some of the most unsavoury characters (5)
I believe the answer is:
stuns
'knocks out' is the definition.
(I've seen this in another clue)
'some of the most unsavoury characters' is the wordplay.
'some of' says the answer is hidden in the clue.
'STUNS' is hidden within 'most unsavoury characters'.
(Other definitions for stuns that I've seen before include "Greatly surprises" , "Bruises" , "Astounds" , "Dazes, stupefies" .)