Bullfighter to bash in back (8)
I believe the answer is:
'bullfighter' is the definition.
(I know that bullfighter can be written as toreador)
'to bash in back' is the wordplay.
'bash' becomes 'do' (synonyms).
'in' is an insertion indicator.
'back' becomes 'rear' (something's rear is its back).
'do' placed inside 'rear' is 'reador'.
(Other definitions for toreador that I've seen before include "Adore rot (anag)" , "Too drear for a bullfighter" , "killer on mount" , "Bullfighter in Carmen" , "One who fights bulls" .)