Spoil stuff on the way back (3)
I believe the answer is:
mar
'spoil' is the definition.
('mar' can be a synonym of 'spoil')
'stuff on the way back' is the wordplay.
'stuff' becomes 'ram' (ramming is a kind of stuffing).
'on the way back' says the letters should be written backwards.
'ram' backwards is 'MAR'.
(Other definitions for mar that I've seen before include "A windy month" , "Spoil something" , "Spoil stuff" , "'Damage, impair (3)'" , "wreck" .)