The most common and most likely answer to this crossword clue is the 12 letter word OBSTREPEROUS
I've seen this crossword clue in Financial Times
O
B
S
T
R
E
P
E
R
O
U
S
More clues leading to the result OBSTREPEROUS
- Unruly old boy upset superstore
- Drunk sups root beer, becoming rough and rowdy
- Rowdy Robert in trouble with spouse
- Unruly, awkward spouse Robert
- Set super booster to ‘loud’
- Rowdy Peter’s arranged run out in old coach
- Noisy old transport carrying poster designed to include queen
- Bloody-minded old boy found in front of new superstore
- Drunken bore’s posture becomes unruly
- Stroppy pros, to be sure, may be retrained
Buddy explains!

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 OBSTREPEROUS mean?
OBSTREPEROUS adjective- Attended by, or making, a loud and tumultuous noise; boisterous.
- Stubbornly defiant; disobedient; resistant to authority or control, whether in a noisy manner or not.