Duck when beer mugs are thrown around (8)

I believe the answer is:

submerge

I'm a little stuck... Click here to teach me more about this clue!

'duck' is the definition.
(I've seen this before)

'beer mugs are thrown around' is the wordplay.
'beer mugs' anagrams to 'SUBMERGE'.
Though, I am not clear how this is indicated.

'when' acts as a link.

Can you help me to learn more?

(Other definitions for submerge that I've seen before include "Cover" , "Sink - inundate" , "swill round" , "(Submarine) dive" , "Put under water" .)

I've seen this clue in The Globe and Mail.

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