Punch a mate (5)
I believe the answer is:
china
'mate' is the definition.
(cockney rhyming slang, mate is china plate)
'punch a' is the wordplay.
'punch' becomes 'chin' (slang term meaning to punch someone on the chin).
'chin'+'a'='CHINA'
(Other definitions for china that I've seen before include "Oriental country" , "Hi, can you make porcelain here?" , "Tableware; country" , "Porcelain articles" , "Where one regularly unloads junk" .)