The most common and most likely answer to this crossword clue is the 11 letter word BLUNDERBUSS
I've seen this crossword clue in The Times
B
L
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N
D
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B
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S
More clues leading to the result BLUNDERBUSS
- Musket son brought into passenger vehicle by mistake
- Clumsy person reported vehicle after slip
- Qualified lawyer, subordinate plonker? It could be fatal
- One launching projectiles knocked over player in the slips
- Big old arm beginning to sweat after trip on public transport
- Makes a faux pas plugging bishop, American, with old handgun
- Errors, including public transport vehicle arm once
- Mistake over kiss? One would have been shot!
- Long ago one fired transport provider to stop silly mistakes
- Tactless remarks about black American's old musket
Buddy explains!

The straight part
We know that "Clumsy person" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clumsy person = blunderbuss.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 BLUNDERBUSS mean?
BLUNDERBUSS noun- An old style of muzzleloading firearm and early form of shotgun with a distinctive short, large caliber barrel that is flared at the muzzle, therefore able to fire scattered quantities of nails, stones, shot, etc. at short range.
- To shoot with a blunderbuss.