The most common and most likely answer to this crossword clue is the 13 letter word CONTRAVENTION
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The straight part
We know that "Violation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case violation = contravention.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.
Crossword Answer definitions
CONTRAVENTION noun- The act of contravening a rule, regulation, or law, or of not fulfilling an obligation, promise, or agreement.