Good indoor workers maybe heading off to be field workers (8)

I believe the answer is:

gleaners

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'workers' is the definition.
(gleaner is a kind of worker)

'good indoor workers maybe heading off to be field' is the wordplay.
I cannot quite see how this works, but
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
'be' could be 'lean' (leaning is a kind of being) and 'lean' is found in the answer.
The remaining letters 'ers' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Telegraph.

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