Trophy remains held by you, once foremost in sport (3,5)
I believe the answer is:
the ashes
'trophy' is the definition.
(cricket trophy)
'remains held by you once foremost in sport' is the wordplay.
'remains' becomes 'ash' (remains of a fire).
'held by' indicates putting letters inside.
'you once' becomes 'thee' (historical second person pronoun).
'foremost in' says to take the initial letters.
The first letter of 'sport' is 's'.
'ash' inserted within 'thee' is 'theashe'.
'theashe'+'s'='THE ASHES'
(Other definitions for the ashes that I've seen before include "Cricketing trophy" , "Trophy for winner of AngloAustralian cricket series" , "Trophy awarded in England-Australia cricket, sounds grubby" , "trees" .)