Bowled? Bother -- this drops (4)
I believe the answer is:
bail
'this drops' is the definition.
(part of a cricket wicket)
'bowled? bother' is the wordplay.
'bowled?' becomes 'b' (cricket abbreviation).
'bother' becomes 'ail' (I've seen this before**).
'b'+'ail'='BAIL'
(Other definitions for bail that I've seen before include "Wooden bar" , "Surety - part of wicket - scoop" , "Piece placed on top of cricket stumps" , "Item resting on stumps" , "small bar on field" .)