Qualification as cowboy, say? (5)

I believe the answer is:

rider

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'qualification' is the definition.
(qualification or condition in a contract)

I cannot understand how the rest of the clue works.

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(Other definitions for rider that I've seen before include "Contract clause" , "One who's got up" , "Equestrian added by a jury?" , "Horseman or cyclist" , "in the dressing room before the show?" .)

I've seen this clue in The Guardian.

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