Sudden movement scared youngster (6,7)

I believe the answer is:

spring chicken

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'youngster' is the definition.
(an older person is 'no spring chicken')

'sudden movement scared' is the wordplay.
'sudden movement' becomes 'spring' (I can't explain this - if you can you should give a lot more credence to this answer).
'scared' becomes 'chicken'.
'spring'+'chicken'='SPRING CHICKEN'

Can you help me to learn more?

(Other definitions for spring chicken that I've seen before include "Young (bird or) person" , "Young person (as seen by an old person)" , "Young bird (used as disparaging comparison with older people)" , "Youngster" , "Fowl - type of youth" .)

I've seen this clue in The Telegraph.

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