Damage small vehicle (4)
I believe the answer is:
scar
'damage' is the definition.
(I know that scar is a type of blemish)
'small vehicle' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'vehicle' becomes 'car' (car is a kind of vehicle).
's'+'car'='SCAR'
(Other definitions for scar that I've seen before include "Gordale - - , Yorks" , "Indication of damage" , "Trace of an old injury" , "Steep cliff; skin mark" , "Stigma" .)