Pro's opening two rounds once again rubbish (3-3)

I believe the answer is:

poo-poo

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'again rubbish' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'pro's opening two rounds once' is the wordplay.
'opening' suggests taking the first letters.
'two rounds' becomes 'oo' (two round letters).
'once' becomes 'poo' (I can't justify this - if you can you should give a lot more credence to this answer).
The first letter of 'pros' is 'p'.
'p'+'oo'+'poo'='POO-POO'

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I've seen this clue in The Independent.

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