Show transformed during relegation (13)

I believe the answer is:

demonstration

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'show' is the definition.
(demonstration is a kind of show)

'transformed during relegation' is the wordplay.
'transformed' becomes 'nstra' (I can't justify this - if you can you should believe this answer much more).
'during' means one lot of letters goes inside another.
'relegation' becomes 'demotion' (I've seen this before).
'nstra' inserted within 'demotion' is 'DEMONSTRATION'.

Can you help me to learn more?

(Other definitions for demonstration that I've seen before include "Protest march/meeting" , "Public rally as protest" , "Protest meeting" , "Protest march" , "Exhibition, protest" .)

I've seen this clue in The Guardian.

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