Track used by top athletes (4)
I believe the answer is:
path
'track' is the definition.
('path' can be a synonym of 'track')
'used by top athletes' is the wordplay.
'used by' indicates the answer is hidden within the clue.
'PATH' is hidden in the letters of 'top athletes'.
(Other definitions for path that I've seen before include "Track, way for walkers" , "trail" , "Way for pedestrians" , "Skin on top of head" , "Route, course" .)