Wallop in New Hampshire (4)
I believe the answer is:
wham
'wallop' is the definition.
(I know that wallop can be written as wham)
'in new hampshire' is the wordplay.
'in' indicates a hidden word.
'WHAM' is hidden within 'new hampshire'.
(Other definitions for wham that I've seen before include "Strike -- 1980s' pop group" , "Eighties pop group" , "Sound of heavy blow" , "striker may do so" , "Come down hard on" .)