The most common and most likely answer to this crossword clue is the 9 letter word AFFIDAVIT
I've seen this crossword clue in Independent
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More clues leading to the result AFFIDAVIT
- One’s sworn at, very loudly, girls included
- Statement FIFA put out: US lawyer against it
- A fellow, if climbing crane, supplies legal document
- Tiny vase differed, as halved and returned in statement
- Instrument‘s first-rate hoist absorbing doubled force
- Statement FIFA put out — US lawyer’s opposing it
- Statement’s invalid if David’s fat son and daughter abscond
- A fine fellow and kinky diva with sex appeal produce legal document
Buddy explains!

The straight part
We know that "legal document" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case legal document = affidavit.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 AFFIDAVIT mean?
AFFIDAVIT noun- A signed document wherein an affiant makes a sworn statement.