The most common and most likely answer to this crossword clue is the 9 letter word MOTOCROSS
M
O
T
O
C
R
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S
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More clues leading to the result MOTOCROSS
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 = motocross.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 MOTOCROSS mean?
MOTOCROSS noun- A form of off-road motorbike racing.
- An event where such racing takes place.