Concerning racehorse, raised Cain perhaps (8)
I believe the answer is:
murderer
'cain perhaps' is the definition.
(cain murdered abel in the bible)
'concerning racehorse raised' is the wordplay.
'concerning' becomes 're'.
'racehorse' becomes 'redrum' (three time winner of the Grand National).
'raised' says the letters should be written backwards.
're'+'redrum'='reredrum'
'reredrum' reversed gives 'MURDERER'.
(Other definitions for murderer that I've seen before include "One commits homicide" , "hit man" , "Criminal killer" , "Assassin" , "Deliberate unlawful killer" .)