Last longer than unfashionable sport (7)
I believe the answer is:
outwear
'last longer than' is the definition.
(I've seen this before)
'unfashionable sport' is the wordplay.
'unfashionable' becomes 'out' (synonyms).
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'out'+'wear'='OUTWEAR'
(Other definitions for outwear that I've seen before include "ride" , "may last longer" , "Exhaust" , "Last longer than others" , "Top dressing" .)