Mix it in the yard (4)

I believe the answer is:

spar

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

I cannot understand how the rest of the clue works.

(Other definitions for spar that I've seen before include "Close friend" , "Box in training - mineral" , "Practise boxing with a pole?" , "Raps with large timber" , "microcrystalline mineral?" .)

I've seen this clue in the Evening Standard.

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