Jockey upsets the foreign horse from America jumping over top of rails for leading trainer (8)
I believe the answer is:
struggle
'leading trainer' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'jockey upsets the foreign horse from america jumping over top of rails' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'horse' could be 'gg' (geegee or GG is a childish term for a horse) and 'gg' is found within the answer.
'from' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for struggle that I've seen before include "pains" , "Wrestle" , "Grapple, contend" , "Contend; very hard task" , "Strenuous effort against odds" .)