One of the bunch has a bit of a black eye! (3)
I believe the answer is:
key
'one of the bunch' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'a bit of a black eye' is the wordplay.
'a bit of' says the answer is hidden in the clue.
'KEY' can be found hidden inside 'black eye'.
'has' acts as a link.
Can you help me to learn more?
(Other definitions for key that I've seen before include "Coral reef off southern coast of Florida" , "A major say" , "Clue" , "//www.crosswordgiant.com/crossword-clue/1252911/" , "Crucially important" .)