Crook caught at end of Ramadan in Asian sultanate (6)
I believe the answer is:
conman
'crook' is the definition.
(I know that crook can be written as conman)
'caught at end of ramadan in asian sultanate' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'at end of' says to take the final letters.
'in' indicates putting letters inside.
'asian sultanate' becomes 'Oman' (Oman is a sultanate).
The last letter of 'ramadan' is 'n'.
'n' going within 'oman' is 'onman'.
'c'+'onman'='CONMAN'
(Another definition for conman that I've seen is " who's full of tricks?".)