Support team that's behind (8)
I believe the answer is:
'behind' is the definition.
('backside' can be a synonym of 'behind')
'support team' is the wordplay.
'support' becomes 'back' (back is a kind of support).
'team' becomes 'side' (I've seen this before).
'that's' acts as a link.
(Other definitions for backside that I've seen before include "Buttocks" , "Seat" , "Bottom" , "Behind" , "Rear" .)