Fly in reverse to get a kick (4)
I believe the answer is:
tang
'a kick' is the definition.
(a strong taste or smell)
'fly in reverse' is the wordplay.
'fly' becomes 'gnat' (type of insect).
'in reverse' shows that the letters should be reversed in order.
'gnat' in reverse letter order is 'TANG'.
'to get' acts as a link.
(Other definitions for tang that I've seen before include "Aroma" , "The biting flavour of seaweed" , "tastefulness" , "Thrash with good" , "Piquancy - Chinese dynasty" .)