The most common and most likely answer to this crossword clue is the 9 letter word PRECEDENT
I've seen this crossword clue in The Guardian
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More clues leading to the result PRECEDENT
- Go back into press's first books for a previous case
- Before Christ impressed Mark, providing an example for followers
- Repented being wrong about a key earlier legal case
- Pressure on editor in new test case
- Quiet journalist in new influential legal decision
- What in the Bible OT must do, giving earlier example
- Model perhaps repented snorting cocaine
- Similar instance earlier brought pressure to withdraw book
- Pressure to withdraw conservationists? It’s happened before
- Point about playground garden — an example to be followed
Buddy explains!

The straight part
We know that "It’s happened before" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s happened before = precedent.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 PRECEDENT mean?
PRECEDENT noun- An act in the past which may be used as an example to help decide the outcome of similar instances in the future.
- A decided case which is cited or used as an example to justify a judgment in a subsequent case.
- An established habit or custom.
- (with definite article) The aforementioned (thing).
- The previous version.
- A rough draught of a writing which precedes a finished copy.
- To provide precedents for.
- To be a precedent for.
- Happening or taking place earlier in time; previous or preceding.
- Coming before in a particular order or arrangement; preceding, foregoing.