The most common and most likely answer to this crossword clue is the 11 letter word RUMBUSTIOUS
I've seen this crossword clue in The Times
R
U
M
B
U
S
T
I
O
U
S
Buddy explains!

The straight part
We know that "Unruly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unruly = rumbustious.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 RUMBUSTIOUS mean?
RUMBUSTIOUS adjective- Boisterous and unruly.