Refuse to obey loud yob (5)
I believe the answer is:
flout
'refuse to obey' is the definition.
(as in flouting rules)
'loud yob' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'yob' becomes 'lout' (both can mean an antisocial young man).
'f'+'lout'='FLOUT'
(Other definitions for flout that I've seen before include "Defy (orders etc)" , "Mock" , "Show contempt for, defy" , "Show contempt for (the law)" , "Ignore (rule)" .)