No, not something a showjumper wants? (7)
I believe the answer is:
refusal
'not something a showjumper wants?' is the definition.
(refusal can mean a horse refusing to make a jump)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for refusal that I've seen before include "The turning down of a request" , "Horse's action in declining to jump a fence" , "Stop by fence" , "Being told no to request, will not oblige" , "Declining of an offer" .)