Making a (good?) fist of passing over legal document (11)

I believe the answer is:

handwriting

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'making a good? fist' is the definition.
I can't judge whether this definition defines the answer.

'passing over legal document' is the wordplay.
'passing' becomes 'handing' ('hand' can be a synonym of 'pass').
'over' is an insertion indicator.
'legal document' becomes 'writ' (writ is a kind of legal document).
'handing' placed around 'writ' is 'HANDWRITING'.

'of' is the link.

Can you help me to learn more?

(Another definition for handwriting that I've seen is " That which is studied by a calligrapher".)

I've seen this clue in The Telegraph.

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