Crime pertaining to criminal (7)
I believe the answer is:
offence
'crime' is the definition.
(I know that crime can be written as offence)
'pertaining to criminal' is the wordplay.
'pertaining to' becomes 'of' (I can't explain this - if you can you should give a lot more credence to this answer).
'criminal' becomes 'fence' (I've seen this in other clues).
'of'+'fence'='OFFENCE'
Can you help me to learn more?
(Other definitions for offence that I've seen before include "Attack - crime" , "Misdeed" , "Hurting of feelings" , "Discourtesy" , "An act punishable by law" .)