Boy brought up as a lout (3)
I believe the answer is:
yob
'a lout' is the definition.
(both can mean a rude or criminal young person)
'boy brought up' is the wordplay.
'brought up' is a reversal indicator (in a down clue, letters go up).
'boy' written backwards gives 'YOB'.
'as' acts as a link.
(Other definitions for yob that I've seen before include "Rude aggressive youth" , "Thug" , "Loutish young man" , "Hooligan kind of boy" , "Lout (sl.)" .)