The most common and most likely answer to this crossword clue is the 9 letter word MOTOCROSS
I've seen this crossword clue in The Guardian
M
O
T
O
C
R
O
S
S
More clues leading to the result MOTOCROSS
Buddy explains!

The straight part
We know that "sporting event" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sporting event = 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.