Spoil copper's boy (6)
I believe the answer is:
marcus
'boy' is the definition.
(I've seen this before)
'spoil copper's' is the wordplay.
'spoil' becomes 'mar' (I've seen this before).
'copper's' becomes 'cus' (chemical symbol).
'mar'+'cus'='MARCUS'
(Other definitions for marcus that I've seen before include "Man" , "chap" , "boy" .)