Common racetrack shape (4)
I believe the answer is:
oval
'common racetrack shape' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oval that I've seen before include "Where a duck may be broken" , "Cricket ground - presidential office" , "Race track" , "London cricket-ground" , "34 [CRICKETER] 's domain" .)