Convict taking circuitous route to welcome large young man, violent when drunk (5,4)
I believe the answer is:
lager lout
'young man violent when drunk' is the definition.
'convict taking circuitous route to welcome large' is the wordplay.
'convict' becomes 'lag' (I've seen this before).
'taking' says to put letters next to each other.
'circuitous' is an anagram indicator.
'to welcome' means one lot of letters goes inside another (in sense of 'inviting in').
'large' becomes 'l'.
'route' anagrammed gives 'erout'.
'erout' placed around 'l' is 'erlout'.
'lag'+'erlout'='LAGER LOUT'
(Other definitions for lager lout that I've seen before include "Troublesome drunk" , "Drinker behaving antisocially" , "Boozy yob" , "anti-social sort" , "Alcohol-fuelled youth" .)