Be at, and drink from, mugs (5,2)

I believe the answer is:

beats up

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'mugs' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how one could define the other.

'be at and drink' is the wordplay.
'and' is a charade indicator (letters next to each other).
'drink' becomes 'sup' (to sup is to drink).
'be'+'at'+'sup'='BEATS UP'

'from' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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