Criminal rules a con could be light-fingered (9)
I believe the answer is:
larcenous
'be light-fingered' is the definition.
'criminal rules a con' is the wordplay.
'criminal' indicates anagramming the letters.
'rules'+'a'+'con'='rulesacon'
'rulesacon' anagrammed gives 'LARCENOUS'.
'could' is the link.
(Other definitions for larcenous that I've seen before include "Criminal" , "Thievish" , "Like other crimes" , "With sticky fingers" , "concerning certain crimes" .)