Within a fashionable team (6)
I believe the answer is:
inside
'within' is the definition.
(synonyms)
'a fashionable team' is the wordplay.
'a fashionable' becomes 'in' (in can mean fashionable or trendy).
'team' becomes 'side' (both can mean a sports team).
'in'+'side'='INSIDE'
(Other definitions for inside that I've seen before include "Inner surface" , "banged up" , "Not external, perhaps in prison" , "locked up" , "Enid is (anag) - within" .)