Badly behaved child runs into club (4)
I believe the answer is:
brat
'badly behaved child' is the definition.
(I've seen this before)
'runs into club' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'into' is an insertion indicator.
'club' becomes 'bat' (bat is a kind of club).
'r' put into 'bat' is 'BRAT'.
(Other definitions for brat that I've seen before include "child - that's a nuisance" , "Irritating youngster" , "Marie ---, birth-control pioneer" , "Very dry" , "Spoilt kid" .)