Servant grabbed by heartless brute, resulting in injury (5,3)
I believe the answer is:
black eye
'resulting in injury' is the definition.
'servant grabbed by heartless brute' is the wordplay.
'servant' becomes 'lackey' (a lackey is a servant or assistant).
'grabbed by' indicates putting letters inside (inserted letters are grabbed inside).
'heartless' suggests removing the centre.
'brute' with its middle taken out is 'be'.
'lackey' placed within 'be' is 'BLACK EYE'.
(Other definitions for black eye that I've seen before include "Kind of bruise - kind of bean" , "fight evidence" , "result of being punched?" , "Bruised facial area" , "Result of facial blow" .)