Crossword Genius

What certain thieves do in Ulster? (6)

Ross

I believe the answer is:

rustle

I'm a little stuck... Click here to teach me more about this clue!

'what certain thieves do' is the definition.
The definition suggests a singular noun which matches the answer.

'ulster?' is the wordplay.
'ulster' can be anagrammed to 'RUSTLE'.
But, I'm not clear how this is indicated.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for rustle that I've seen before include "Steal cattle in the old West" , "Steal stock" , "Wind-in-leaves noise" , "Result (anag.)" , "Low sound of rubbing" .)

I've seen this clue in the Evening Standard.
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