Sign of injury on a black beetle (6)
I believe the answer is:
scarab
'beetle' is the definition.
(scarab is a kind of beetle)
'sign of injury on a black' is the wordplay.
'sign of injury' becomes 'scar' (I've seen this before).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'black' becomes 'b' (abbreviation as in pencil hardness).
'scar'+'a'+'b'='SCARAB'
(Other definitions for scarab that I've seen before include "insect" , "Beetle considered divine by ancient Egyptians" , "Sacred Egyptian beetle" , "Sacred beetle of Eygpt" , "divine thing once" .)