Remains bored, withdrawing our team's boxing debut at last (8)
I believe the answer is:
detritus
'remains' is the definition.
(I've seen this before)
'bored withdrawing our team's boxing debut at last' is the wordplay.
'bored' becomes 'tired' (similar in meaning).
'withdrawing' says the letters should be written backwards.
'our team' becomes 'us'.
'boxing' is an insertion indicator ('box' can mean contain, as in to put in a box).
'at last' suggests the final letters.
The final letter of 'debut' is 't'.
'tired' back-to-front is 'derit'.
'derit'+'us'='deritus'
'deritus' placed around 't' is 'DETRITUS'.
(Other definitions for detritus that I've seen before include "Loose eroded matter" , "Accumulation of debris - it rusted (anag)" , "More 22 Across, gravel made by erosion" , "Loose material worn away from rocks" , "Refuse" .)