Flip down and start? Just the opposite! (5)

I believe the answer is:

upend

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

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

(Other definitions for upend that I've seen before include "Flip" , "Topple" , "Overturn" , "Turn upside-down" , "Turn top to bottom" .)

I've seen this clue in The Guardian.

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