The most common and most likely answer to this crossword clue is the 9 letter word INFORMERS
I've seen this crossword clue in The Daily Telegraph
I
N
F
O
R
M
E
R
S
More clues leading to the result INFORMERS
Buddy explains!
The straight part
We know that "Rats" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rats = informers.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 INFORMERS mean?
INFORMERS noun- One who informs someone else about something.
- A person who tells authorities about improper or illegal activity.
- One who informs, animates, or inspires.