Thrust the wrong way and spoil (3)
I believe the answer is:
mar
'spoil' is the definition.
('mar' can be a synonym of 'spoil')
'thrust the wrong way' is the wordplay.
'thrust' becomes 'ram' (ramming is a kind of thrusting).
'the wrong way' shows that the letters should be reversed in order.
'ram' reversed gives 'MAR'.
'and' acts as a link.
(Other definitions for mar that I've seen before include "Spanish main?" , "Spoil, damage" , "Spoil stuff" , "Spoil something" , "A windy month" .)