One to beat clubs in bid for sports field (7)

I believe the answer is:

diamond

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'field' is the definition.
(I know that diamond is a type of field)

I don't understand how the rest of the clue works.

(Other definitions for diamond that I've seen before include "that might be useful in dating?" , "Red card" , "rock hard" , "Birthstone for April" , "Very hard gem" .)

I've seen this clue in The Times.

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