Return a bear to the ring (4)
I believe the answer is:
hoop
'the ring' is the definition.
('hoop' can be a synonym of 'ring')
'return a bear' is the wordplay.
'return' is a reversal indicator.
'a bear' becomes 'pooh' (Winnie the Pooh).
'pooh' backwards is 'HOOP'.
'to' is the link.
(Other definitions for hoop that I've seen before include "Metal ring for croquet and basketball" , "Rigid circular band" , "Wood, metal or plastic band" , "Circlet" , "Arch used in croquet" .)