Punch a fragile thing (5)
I believe the answer is:
china
'fragile thing' is the definition.
(as in porcelain china)
'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 "Porcelain ware and country" , "set of porcelain" , "Delicate porcelain from Cathay?" , "Where one regularly unloads junk" , "Fine earthenware" .)