Support team that's behind (8)
I believe the answer is:
backside
'behind' is the definition.
(synonyms)
'support team' is the wordplay.
'support' becomes 'back' (to back is to support or endorse).
'team' becomes 'side' (both can mean a sports team).
'back'+'side'='BACKSIDE'
'that's' is the link.
(Other definitions for backside that I've seen before include "Buttocks" , "Seat" , "Bottom" , "Behind" , "Rear" .)