It involves guesswork to crack hard case (8)

I believe the answer is:

charades

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'it involves guesswork' is the definition.
The definition suggests a singular noun which matches the answer.

'crack hard case' is the wordplay.
'crack' indicates anagramming the letters.
'hard'+'case'='hardcase'
'hardcase' is an anagram of 'CHARADES'.

'to' acts as a link.

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(Other definitions for charades that I've seen before include "Games like this" , "Miming parlour game" , "Guessing game where words are acted out" , "Party guessing game" , "Game in which answers are acted out" .)

I've seen this clue in The Guardian.

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