The most common and most likely answer to this crossword clue is the 9 letter word BRIDLEWAY
I've seen this crossword clue in Financial Times
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More clues leading to the result BRIDLEWAY
Buddy explains!
The straight part
We know that "trail of jumpers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trail of jumpers = bridleway.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BRIDLEWAY mean?
BRIDLEWAY noun- A path for riding a horse (which is controlled by a bridle).
- A right of way defined in law, over which the public have the right to travel on foot or on horseback or leading a horse, with or without a right to drive animals of any description along the way.