Crossword Genius

Surplus bowling ball (9)

Ross

I believe the answer is:

overspill

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'ball' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Perhaps you can see a link between them that I don't see?

'surplus bowling' is the wordplay.
'surplus' becomes 'over' (I've seen this before).
'bowling' becomes 'spill' (I am not sure about this - if you are sure you should believe this answer much more).
'over'+'spill'='OVERSPILL'

Can you help me to learn more?

(Other definitions for overspill that I've seen before include "for people moving out of slums?" , "Surplus population moving elsewhere" , "excessive amount" , "Excess; surplus (population)" , "Excess liquid" .)

I've seen this clue in The Independent.
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