Support; football player (4)
I believe the answer is:
back
This clue is a double definition.
'support' is the first definition.
(to back is to support or endorse)
'football player' is the second definition.
(back is a kind of football player)
(Other definitions for back that I've seen before include "See 17" , "Golf holes 10-18" , "defensive player" , "player in line of defence?" , "Rear; spine" .)