Crossword Genius

At snooker halls, they roll around in hundreds (4)

Ross

I believe the answer is:

reds

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'at snooker' is the definition.
Although both the answer and 'snooker' are nouns, they are not in the same form of the noun. However, I know that 'snooker' relates to this answer.

'halls they roll around in hundreds' is the wordplay.
'REDS' is hidden in amongst the letters.
But, I'm unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for reds that I've seen before include "Scarlet and crimson, say" , "Tidies up" , "Scarlet communists" , "Left-wingers" , "These are not right" .)

I've seen this clue in the Evening Standard.
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