Next to an extensive team (9)
I believe the answer is:
alongside
'next to' is the definition.
(I've seen this before)
'an extensive team' is the wordplay.
'an extensive' becomes 'along' (I can't explain this - if you can you should believe this answer much more).
'team' becomes 'side' (both can mean a sports team).
'along'+'side'='ALONGSIDE'
Can you help me to learn more?
(Other definitions for alongside that I've seen before include "Next to, another boat perhaps" , "Side by side" , "Parallel to" , "Juxtaposed" , "Lying next to, as a boat might be" .)