Mate to punch American (5)
I believe the answer is:
china
'mate' is the definition.
(cockney rhyming slang, mate is china plate)
'punch american' is the wordplay.
'punch' becomes 'chin' (slang term meaning to punch someone on the chin).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'chin'+'a'='CHINA'
'to' acts as a link.
(Other definitions for china that I've seen before include "Porcelain ware and country" , "Tableware; country" , "It used to be called Cathay" , "Cathay was its archaic name" , "Mate (slang); crockery" .)