Down with Oxbridge sportsman (4)
I believe the answer is:
blue
I believe this is a double definition.
'down' is the first definition.
(I've seen this before)
'oxbridge sportsman' is the second definition.
(I've seen this before)
'with' is the link.
(Other definitions for blue that I've seen before include "Oxbridge sports award" , "Sad - colour" , "Colour; depressed" , "Sea colour" , "Varsity sportsman" .)