In a position to win game of darts quickly (2,3,6)

I believe the answer is:

on the double

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

'quickly' is the definition.
(I've seen this in another clue)

'in a position to win game of darts' is the wordplay.
I cannot really see how this works, but
'game' could be 'on' (both can mean willing) and 'on' is found in the answer.
'of' could be 'o' and 'o' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Independent.

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