At snooker, they aren't so good as the blacks (4)
I believe the answer is:
reds
'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.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for reds that I've seen before include "Colours for communists" , "Scarlet and crimson, say" , "Tidies up" , "Colourful communists" , "First snooker balls to be potted" .)