Case having been dismissed, criminals cheat at cards (4)
I believe the answer is:
rook
'cheat at cards' is the definition.
(rook can mean a card-game cheat)
'case having been dismissed criminals' is the wordplay.
'case having been dismissed' means to look at the middle letters (the letters which encase the word are removed).
'criminals' becomes 'crooks' ('crook' can be a synonym of 'criminal').
The centre of 'crooks' is 'ROOK'.
(Other definitions for rook that I've seen before include "Ringing in the ears" , "Gregarious black bird" , "Black bird - cheat - chess piece" , "Swindle; castle" , "Fleece - bird" .)