Some criminals to parley in bar (4)
I believe the answer is:
stop
'bar' is the definition.
(bar can mean to stop or prevent)
'some criminals to parley' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'STOP' is hidden within 'criminals to parley'.
'in' acts as a link.
(Other definitions for stop that I've seen before include "Post (anag.)" , "Finished" , "Red light signal" , "high card in bridge" , "Knock out" .)