Cuts top off sporting trophy (5)
I believe the answer is:
ashes
'sporting trophy' is the definition.
(I've seen this before)
'cuts top off' is the wordplay.
'cuts' becomes 'gashes' ('gash' can be a synonym of 'cut').
'top off' means to remove the first letter.
'gashes' with its initial letter removed is 'ASHES'.
(Other definitions for ashes that I've seen before include "sporting trophy" , "Remains from a cremation" , "Cricketing trophy - remains" , "Former Wimbledon champion's" , "''... to ..., dust to dust'' (burial service)" .)