Rule announced for horse riding gear (4)
I believe the answer is:
rein
'gear' is the definition.
(rein is a kind of gear)
'rule announced' is the wordplay.
'rule' becomes 'reign' (reign is a kind of rule).
'announced' shows a homophone (sound like).
'reign' is a homophone of 'REIN'.
'for horse riding' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rein that I've seen before include "Free ... is carte blanche" , "Animal controller" , "kidney?" , "Strap to control horse" , "(Horse's) guiding strap" .)