Enthusiastic cry of a youngster following a race (7)

I believe the answer is:

attaboy

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'enthusiastic cry of a youngster following a race' is the definition.
I can't tell whether this defines the answer.

'a youngster following a race' is the wordplay.
'youngster' becomes 'boy' (I've seen this in another clue).
'following' says to put letters next to each other.
'race' becomes 'tt'.
'a'+'boy'='aboy'
'a'+'tt'='att'
'aboy' after 'att' is 'ATTABOY'.

Can you help me to learn more?

(Other definitions for attaboy that I've seen before include "What's said to encourage" , "Expression of encouragement, Tay boat (anag.)" , "Come on!" , "word of encouragement" .)

I've seen this clue in the Evening Standard.

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