Punch a mate in Cheapside? (5)
I believe the answer is:
china
'mate in cheapside?' is the definition.
(china [plate] is Cockney rhyming slang for 'mate')
'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 "Asian country" , "Delicate porcelain from Cathay?" , "Porcelain articles" , "Ceramics; country" , "porcelain cups?" .)