Federer rival (5)
I believe the answer is:
nadal
'federer rival' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nadal that I've seen before include "Star with a 30 [RACKET]" , "tennis champion" , "Rafael __, Spanish tennis player" , "Top tennis player" , "court figure" .)