Horse race (12)
I believe the answer is:
steeplechase
'horse race' is the definition.
(steeplechase is a kind of horse race)
This is the entire clue.
(Other definitions for steeplechase that I've seen before include "Horse race with ditches and hedges" , "Non-flat horse race" , "run?" , "Running event over hurdles and water jumps" , "Maybe Grand National" .)