The most common and most likely answer to this crossword clue is the 9 letter word AMBUSCADE
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More clues leading to the result AMBUSCADE
Buddy explains!

The straight part
We know that "attack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case attack = ambuscade.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 AMBUSCADE mean?
AMBUSCADE noun- An ambush; a trap laid for an enemy.
- The place in which troops lie hidden for an ambush.
- The body of troops lying in ambush.
- To lie in wait for, or to attack from a covert or lurking place; to waylay.