Reserve placed on a team (3,5)
I believe the answer is:
set aside
'reserve' is the definition.
('set aside' can be a synonym of 'reserve')
'placed on a team' is the wordplay.
'placed' becomes 'set' ('set' can be a synonym of 'placed'**).
'on' means one lot of letters go next to another.
'team' becomes 'side' (I've seen this before).
'set'+'a'+'side'='SET-ASIDE'
(Other definitions for set aside that I've seen before include "Farm land taken out of production" , "Reserve(d) in advance" , "Policy for leaving land alone" , "Lay by" , "Fallow" .)