The most common and most likely answer to this crossword clue is the 9 letter word SKYDIVING
I've seen this crossword clue in The Times
S
K
Y
D
I
V
I
N
G
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 = skydiving.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 SKYDIVING mean?
SKYDIVING verb- To be in freefall after jumping from an aircraft and landing safely by deploying a parachute.
- The practice of performing acrobatic movements during the freefall phase of a parachute jump.