Shows impatience, admitting tramp doesn't know the score? (5-5)

I believe the answer is:

sight-reads

'doesn't know the score?' is the definition.
(musical score)

'shows impatience admitting tramp' is the wordplay.
'shows impatience' becomes 'sighs'.
'admitting' means one lot of letters goes inside another.
'tramp' becomes 'tread' (I've seen this before).
'sighs' enclosing 'tread' is 'SIGHT-READS'.

I've seen this clue in The Guardian.

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