Support a play or a player (4)
I believe the answer is:
back
This clue is a triple definition!
'support' is the first definition.
(to back is to support or endorse)
'a play' is the second definition.
(thesaurus)
'or' acts as a link.
'a player' is the third definition.
(I have seen 'defensive player' mean 'back' so perhaps 'player' could also mean 'back')
(Other definitions for back that I've seen before include "part of the body" , "Support; footballer" , "Help!" , "Stern" , "Rear surface of the body" .)