Has the desired effect when the rider takes a tumble (5,3)

I believe the answer is:

comes off

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'has' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Maybe there's an association between them I don't understand?

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

Can you help me to learn more?

(Other definitions for comes off that I've seen before include "Exits" , "works" .)

I've seen this clue in the Evening Standard.

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