The most common and most likely answer to this crossword clue is the 8 letter word TAILWIND
I've seen this crossword clue in Independent
T
A
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L
W
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D
More clues leading to the result TAILWIND
Buddy explains!

The straight part
We know that "gust from behind" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gust from behind = tailwind.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 TAILWIND mean?
TAILWIND noun- A wind that blows in the same direction as the course of an aircraft or ship
- Of wind, to blow on a windmill or wind turbine in such a way that wind pressure is exerted on the wrong side of the sail or turbine assembly.