Rear pinched in dance — smack! (4)
I believe the answer is:
tang
'smack' is the definition.
(I know that smack can be written as tang)
'rear pinched in dance' is the wordplay.
'rear pinched in' means to remove the last letter (the letter at the rear is taken away).
'dance' becomes 'tango' (tangoing is a kind of dancing).
'tango' with its final letter taken away is 'TANG'.
(Other definitions for tang that I've seen before include "Smack" , "Bite" , "Sharp flavour" , "tastefulness" , "Beat, with good" .)