Run taken from excellent ball by youngster? That's routine (4,3,5)
I believe the answer is:
song and dance
'routine' is the definition.
(a theatrical routine)
'run taken from excellent ball by youngster?' is the wordplay.
I cannot quite see how this works, but
'from' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'ball' could be 'dance' (ball can mean an event for dancing) and 'dance' is found in the answer.
This explanation may well be incorrect...
'that's' is the link.
(Other definitions for song and dance that I've seen before include "Elements of musical - fuss" , "Ingredients of musical - fuss" , "Kerfuffle" , "Unnecessary fuss" , "commotion" .)