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 don't understand how they can define each other.

'be at and drink' is the wordplay.
'and' means one lot of letters go next to another.
'drink' becomes 'sup' (to sup is to drink).
'be'+'at'+'sup'='BEATS UP'

'from' is the link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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