Tough material players harden (4-5)

I believe the answer is:

cast-steel

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'tough material' is the definition.
The definition suggests a singular noun which matches the answer.

'players harden' is the wordplay.
'players' becomes 'cast' (group of actors).
'harden' becomes 'steel' (I've seen this in another clue).
'cast'+'steel'='CAST-STEEL'

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

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