Crossword Genius

Gangsters' mode of operation when the bank opens (3)

Ross

I believe the answer is:

mob

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'gangsters'' is the definition.
(mob can mean the Mafia)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for mob that I've seen before include "press round" , "Throng" , "Crime syndicate or disorderly crowd" , "Rabble" , "Mafiosi" .)

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