Mayo youth is somewhat up and down (4)

I believe the answer is:

yoyo

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'up and down' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'mayo youth is somewhat' is the wordplay.
'is somewhat' indicates the answer is hidden within the clue.
'YOYO' is hidden in the letters of 'mayo youth'.

Can you help me to learn more?

(Other definitions for yoyo that I've seen before include "Toy" , "Item on string" , "Plaything" .)

I've seen this clue in The Irish Times.

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