Good riders in trouble show courage, initially (4)
I believe the answer is:
grit
'good' is the definition.
(I know that grit is a type of fortitude)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for grit that I've seen before include "called for on icy roads" , "Courage, small stones" , "Gravel or colloquial courage" , "Pluck; sand particles" , "Coarse stone or sand" .)