Track for an athlete (6)
I believe the answer is:
runner
'for an athlete' is the definition.
(type of athlete)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for runner that I've seen before include "Smuggler; a bean" , "Harrier" , "Viable idea" , "Green vegetable" , "Horse in a race; shoot" .)