Support rear (4)
I believe the answer is:
back
I believe this clue is a double definition.
'support' is the first definition.
(to back is to support or endorse)
'rear' is the second definition.
(I know that rear can be written as back)
(Other definitions for back that I've seen before include "bet" , "Support - rear" , "Golf holes 10-18" , "Support - football player" , "Support - defender - reverse" .)