Some urchin, a perfect scruff (4)
I believe the answer is:
nape
'scruff' is the definition.
(synonyms)
'some urchin a perfect' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'NAPE' is hidden in the letters of 'urchin a perfect'.
(Other definitions for nape that I've seen before include "Back part of the neck" , "It's a pane in the neck" , "Scruff of the neck" , "Girl personifying France" , "sofa" .)