Delinquent criminal has worked to rule (5,4)
I believe the answer is:
lager lout
'delinquent' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'criminal has worked to rule' is the wordplay.
'criminal' becomes 'lag' (slang term for a prisoner).
'has' is a charade indicator (letters next to each other).
'worked' indicates anagramming the letters.
'to'+'rule'='torule'
'torule' is an anagram of 'erlout'.
'lag'+'erlout'='LAGER LOUT'
Can you help me to learn more?
(Other definitions for lager lout that I've seen before include "anti-social sort" , "menace" , "Troublesome drunk" , "Alcohol-fuelled youth" , "Drinker behaving antisocially" .)