Where to win about 40% of games? (5)

I believe the answer is:

wigan

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'where to win about 40% of games?' is the definition.
The definition suggests a singular noun which matches the answer.

'where to win about' is the wordplay.
'where' becomes 'ga' (I can't explain this - if you can you should believe this answer much more).
'about' means one lot of letters goes inside another.
'ga' put within 'win' is 'WIGAN'.

Can you help me to learn more?

(Other definitions for wigan that I've seen before include "Lancashire town" , "Manchester-area town, its Pier, Orwell" , "Lancashire FC" , "Town near Manchester" , "North-western town" .)

I've seen this clue in the Evening Standard.

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