Sunshine proverbially packing a punch? (8)

I believe the answer is:

haymaker

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'a punch?' is the definition.
(I know that haymaker is a type of punch)

I cannot understand how the rest of the clue works.

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(Other definitions for haymaker that I've seen before include "required for one working in the sun?" , "A grass harvester or a heavy punch" , "Powerful blow from grass-cutter?" , "strong punch" , "Farm worker - wild punch" .)

I've seen this clue in the Sydney Morning Herald.

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