The most common and most likely answer to this crossword clue is the 8 letter word HORSEMAN
I've seen this crossword clue in The Sunday Telegraph
H
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More clues leading to the result HORSEMAN
Buddy explains!

The straight part
We know that "Equestrian male" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case equestrian male = horseman.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 HORSEMAN mean?
HORSEMAN noun- A man who rides a horse.
- A soldier on horseback.
- A man skilled in horsemanship.
- A man in charge of work horses.
- A swift-running land crab of the genus Ocypoda, living on the coast of Brazil and the West Indies.
- A West Indian fish of the genus Equetes