Expel everyone attending? (7)

I believe the answer is:

turnout

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'attending?' is the definition.
(I know that turnout is a type of attendance)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for turnout that I've seen before include "number of people coming to meeting" , "Number of people attending an event" , "number of people present" , "Attendance figure" , "assembly" .)

I've seen this clue in The Sun.

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