Satisfy knight in criminal depravity (8)
I believe the answer is:
convince
'satisfy' is the definition.
(I've seen this before)
'knight in criminal depravity' is the wordplay.
'knight' becomes 'n' (chess).
'in' is an insertion indicator.
'criminal' becomes 'con' (abbreviation for 'convict').
'depravity' becomes 'vice' (I've seen this before).
'con'+'vice'='convice'
'n' put within 'convice' is 'CONVINCE'.
(Other definitions for convince that I've seen before include "Win over to your point of view" , "Persuade someone of the truth of something" , "Bring round" , "Be persuasive" , "Persuade, satisfy" .)