The most common and most likely answer to this crossword clue is the 12 letter word DISTURBANCES
I've seen this crossword clue in The Daily Telegraph
D
I
S
T
U
R
B
A
N
C
E
S
Buddy explains!

The straight part
We know that "riots" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case riots = disturbances.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 DISTURBANCES mean?
DISTURBANCES noun- The act of disturbing, being disturbed.
- Something that disturbs.
- A noisy commotion that causes a hubbub or interruption.
- An interruption of that which is normal or regular.
- A serious mental imbalance or illness.