What is a collective noun for robbers?

There isn't a single, widely accepted collective noun for robbers. Here are a few options you could use, depending on the context:

Formal:

* A band of robbers

* A gang of robbers

* A crew of robbers

Informal:

* A pack of robbers

* A mob of robbers

You could also get creative and use a more descriptive noun based on the specific type of robbery:

* A hoard of pirates (for seafaring robbers)

* A den of thieves (for sneaky robbers)

* A posse of outlaws (for robbers on the run)

Ultimately, the best collective noun will depend on the specific situation and the desired tone.