The most common and most likely answer to this crossword clue is the 9 letter word WISE-GUYS
I've seen this crossword clue in The Guardian
W
I
S
E
-
G
U
Y
S
Buddy explains!
The straight part
We know that "US Mafiosi" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case us mafiosi = wise-guys.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.