Last longer than unpopular sport (7)
I believe the answer is:
outwear
'last longer than' is the definition.
(I've seen this before)
'unpopular sport' is the wordplay.
'unpopular' becomes 'out' (similar in meaning).
'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 "Exhaust" , "ride" , "may last longer" , "Top dressing" , "Drain" .)