"500" race, for short (4)
I believe the answer is:
indy
'500 race for short' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for indy that I've seen before include "Abandon, discard" , "Type of motor racing" , "US form of motor racing" , "- - Car racing (in US)" , "500-mile US motorcar race" .)