Eject Jack from tournament (4)

I believe the answer is:

oust

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

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

(Other definitions for oust that I've seen before include "Force out; supplant" , "Remove and replace" , "Get rid of" , "Expel - eject" , "Expel (from a place)" .)

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