Night-time criminal backing circle with Capone (9)
I believe the answer is:
nocturnal
'night-time' is the definition.
(I've seen this before)
'criminal backing circle with capone' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'backing' says the letters should be written in reverse.
'circle' becomes 'turn' (**).
'with' says to put letters next to each other.
'capone' becomes 'al'.
'con' in reverse letter order is 'noc'.
'noc'+'turn'+'al'='NOCTURNAL'
(Other definitions for nocturnal that I've seen before include "Like a piece by Chopin?" , "going abroad furtively?" , "Active after dark" , "happening at night" , "Like owls and badgers" .)