Dandy clutching large bomb (4)
I believe the answer is:
flop
'bomb' is the definition.
(I've seen this before)
'dandy clutching large' is the wordplay.
'dandy' becomes 'fop' ('fop' can be a synonym of 'dandy').
'clutching' is an insertion indicator.
'large' becomes 'l'.
'fop' placed around 'l' is 'FLOP'.
(Other definitions for flop that I've seen before include "Dud - bomb" , "Fail" , "Theatrical failure" , "crash" , "Community cards in poker" .)