The most common and most likely answer to this crossword clue is the 7 letter word TEARGAS
I've seen this crossword clue in Financial Times
T
E
A
R
G
A
S
Buddy explains!

The straight part
We know that "riot control measure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case riot control measure = teargas.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 TEARGAS mean?
TEARGAS noun- Any lachrymatory, non-lethal chemical compound that causes the eyes to sting and water and/or irritates the respiratory system, mostly used for controlling crowds during riots or as self-defense.
- To use tear gas.