The most common and most likely answer to this crossword clue is the 12 letter word KITEBOARDING
I've seen this crossword clue in The Guardian
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More clues leading to the result KITEBOARDING
Buddy explains!

The straight part
We know that "sport" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sport = kiteboarding.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 KITEBOARDING mean?
KITEBOARDING noun- A sport in which participants ride a form of wakeboard or surfboard harnessed to a large kite which is controlled by the rider.
- A similar sport using a wheeled board on land.
- A similar sport using a snowboard or ski on snow.