Horse racing establishment ultimately in decline (8)
I believe the answer is:
trotting
'horse' is the definition.
(trotting horse is a kind of horse)
'racing establishment ultimately in decline' is the wordplay.
I cannot quite understand how this works, but
'in' is within the answer.
'decline' could be 'rot' (I've seen this before) and 'rot' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for trotting that I've seen before include "horse-riding?" , "Form of horse racing" , "Harness racing" , "equestrian sport" , "maintaining steady pace" .)