Badly behaved child (4)
I believe the answer is:
brat
'badly behaved child' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for brat that I've seen before include "child - that's a nuisance" , "Annoying child" , "An obnoxious or spoiled child" , "Marie ---, birth-control pioneer" , "Nasty little kid" .)