Attacks those who, dead tired, take refreshment? (5,2)

I believe the answer is:

beats up

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'attacks those who dead' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot see how they can define each other.

'tired take refreshment?' is the wordplay.
'tired' becomes 'beat' (similar in meaning).
'take refreshment?' becomes 'sup' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'beat'+'sup'='BEATS UP'

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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