Support for new setter? (4,2)

I believe the answer is:

prop up

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'support' is the definition.
(I know that prop up is a kind of support)

'for new setter?' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'new setter?' becomes 'pup' (I can't explain this - if you can you should believe this answer much more).
'pro'+'pup'='PROP UP'

Can you help me to learn more?

(Other definitions for prop up that I've seen before include "Give financial backing" , "Underpin" , "Support" , "Keep going" .)

I've seen this clue in The Telegraph.

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