Support beginning to turn for jackanapes (4)
I believe the answer is:
brat
'jackanapes' is the definition.
(I've seen this in another clue)
'support beginning to turn' is the wordplay.
'support' becomes 'bra' (a support for the breasts).
'beginning to' says to take the initial letters.
The first letter of 'turn' is 't'.
'bra'+'t'='BRAT'
'for' is the link.
(Other definitions for brat that I've seen before include "Horrible child" , "Troublesome child" , "Irritating youngster" , "A spoiled badly-behaved child" , "Ill-mannered child" .)