Warned unruly boy (6)
I believe the answer is:
andrew
'boy' is the definition.
'warned unruly' is the wordplay.
'unruly' indicates an anagram.
'warned' anagrammed gives 'ANDREW'.
(Other definitions for andrew that I've seen before include "- - Marr (TV)" , "Wander (anag)" , "apostle" , "Warden (anag.)" , "Scotland's patron saint" .)