The ___ , (horse racing) (4)
I believe the answer is:
turf
'the horse racing' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for turf that I've seen before include "Surface of matted grass - horse racing" , "Piece of lawn" , "Slab for lawn" , "Horseracing as an industry" , "Bit of grass with roots and earth" .)