Crossword Genius

Racketeer shortly receiving cheers about to join in league (8)

Ross

I believe the answer is:

federate

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'in league' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

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(Other definitions for federate that I've seen before include "Join in a league" , "Form an alliance" , "United" .)

I've seen this clue in The Guardian.
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