Crossword Genius

Quiet by perimeter — until one shows up! (7)

Ross

I believe the answer is:

shouter

'perimeter until one shows up' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'quiet by' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'by' becomes 'outer' (I can't justify this - if you can you should believe this answer much more).
'sh'+'outer'='SHOUTER'

(Another definition for shouter that I've seen is " loudmouth".)

I've seen this clue in The Guardian.
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