Crossword Genius

A betrayal that will pack the theatre (4-3)

Ross

I believe the answer is:

sell-out

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

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

'will pack the theatre' is the wordplay.
I cannot quite understand how this works, but
'will' could be 'll' (contracted form, as in 'he'll' - 'he will') and 'll' is found within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

'that' acts as a link.

Can you help me to learn more?

(Other definitions for sell-out that I've seen before include "Event with no further ticket availability" , "successful show" , "Betrayal" , "When all tickets are booked in advance" .)

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