Equestrian qualification (5)
I believe the answer is:
rider
I believe this clue is a double definition.
'equestrian' is the first definition.
(I've seen this in another clue)
'qualification' is the second definition.
(qualification or condition in a contract)
(Other definitions for rider that I've seen before include "Equestrian addition by a jury" , "Condition added to something already agreed" , "Horseman or add-on verdict by jury" , "qualification" , "recommendation made in court" .)