Yahoo's criminal finally released (4)
I believe the answer is:
lout
'yahoo's' is the definition.
(I've seen this in another clue)
'criminal finally released' is the wordplay.
'finally' suggests the final letters.
'released' becomes 'out' (eg out of prison).
The final letter of 'criminal' is 'l'.
'l'+'out'='LOUT'
(Other definitions for lout that I've seen before include "A coarse ill-mannered fellow" , "Yobbo" , "Antisocial person" , "Awkward and stupid person" , "Together" .)