Trendy team locked up (6)
I believe the answer is:
inside
'locked up' is the definition.
(I've seen this before)
'trendy team' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'team' becomes 'side' (both can mean a sports team).
'in'+'side'='INSIDE'
(Other definitions for inside that I've seen before include "Privileged" , "Imprisoned" , "Behind bars (sl.)" , "(Of information) from a confidential source" , "Enid is (anag) - within" .)