Leave a mark (4)
'leave a mark' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scar that I've seen before include "Trace of an old injury" , "Fish" , "Sign of old injury" , "Gordale - - , Yorks" , "reminder of sword-fight?" .)
(Other definitions for bruise that I've seen before include "Rubies (anag.)" , "Impact injury" , "Contusion" , "Skin injury" , "Discolour" .)