Rider to move quickly during downpour (10)
I believe the answer is:
showjumper
'rider' is the definition.
(showjumper is a type of horse rider)
'move quickly during downpour' is the wordplay.
'move quickly' becomes 'jump' (I've seen this in another clue).
'during' indicates putting letters inside.
'downpour' becomes 'shower' (I have seen 'Short downpour ' mean 'shower' so perhaps 'downpour' could also mean 'shower').
'jump' inserted into 'shower' is 'SHOWJUMPER'.
'to' is the link.
(Other definitions for showjumper that I've seen before include "Sportsman" , "one using mount?" , "Sportsperson penalised for a refusal" , "equestrian" , "performer in event" .)