Lad turns up with his behaviour initially bad and loutish (7)
I believe the answer is:
yobbish
'loutish' is the definition.
(I've seen this before)
'lad turns up with his behaviour initially bad' is the wordplay.
'lad' becomes 'boy' (I've seen this before**).
'turns up' is a reversal indicator.
'with' is a charade indicator (letters next to each other).
'initially' suggests taking the first letters.
'bad' indicates an anagram.
The first letter of 'behaviour' is 'b'.
'boy' backwards is 'yob'.
'his'+'b'='hisb'
'hisb' is an anagram of 'bish'.
'yob'+'bish'='YOBBISH'
'and' acts as a link.
(Other definitions for yobbish that I've seen before include "Like a lout" , "characteristic of a lout" , "Behaving badly" , "rudely aggressive" , "Ill-bred" .)