Damage second vehicle (4)
I believe the answer is:
scar
'damage' is the definition.
(I've seen this before)
'second vehicle' is the wordplay.
'second' becomes 's' (common abbreviation).
'vehicle' becomes 'car' (car is a kind of vehicle).
's'+'car'='SCAR'
(Other definitions for scar that I've seen before include "Mark left on healed tissue" , "Mark of healed cut" , "reef" , "Effect of unpleasant experience" , "Skin mark; bare crag" .)