Shock for a criminal (4)
I believe the answer is:
afro
'shock' is the definition.
(I've seen this before)
'for a criminal' is the wordplay.
'criminal' indicates anagramming the letters.
'for'+'a'='fora'
'fora' with letters rearranged gives 'AFRO'.
(Other definitions for afro that I've seen before include "Hairdo of the 1960s and 70s" , "Hairstyle with tight curls" , "Curly hairstyle" , "Hairstyle adopted by the young Michael Jackson" , "Roundish hairstyle" .)