The most common and most likely answer to this crossword clue is the 9 letter word APOLOGIST
I've seen this crossword clue in The Guardian
A
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More clues leading to the result APOLOGIST
- One'll defend a point after game
- Champion making an essential point about game
- Argumentative defender I grabbed by attacked goalpost
- One defending a game point
- Advocate appearing as a famous explorer gains essential point
- Champion provides a game summary
- See serving man in a job as defensive figure
- One might justify a sport with substance
- Defender gets a game point
- Defender god denied one of two students essential meaning
Buddy explains!

The straight part
We know that "One might justify/One might justify" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one might justify/one might justify = apologist.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 APOLOGIST mean?
APOLOGIST noun- One who makes an apology.
- One who speaks or writes in defense of a faith, a cause, or an institution.