The most common and most likely answer to this crossword clue is the 9 letter word FROGMARCH
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "Unceremonious arrest method" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unceremonious arrest method = frogmarch.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 FROGMARCH mean?
FROGMARCH noun- The process of frogmarching a person.
- To march or force a person forward while holding their arms from behind or the side, as a prisoner.
- To force a person forward against their will.
- (formerly) To carry a person face-down with one person holding each limb.
- To forcibly relocate a person, especially in a degrading or humiliating manner.