Stephen Ball is off to sing (5,3,5)
I believe the answer is:
spill the beans
'to sing' is the definition.
(I've seen this before)
'stephen ball is off' is the wordplay.
'off' is an anagram indicator.
'stephen'+'ball'+'is'='stephenballis'
'stephenballis' is an anagram of 'SPILL THE BEANS'.
(Other definitions for spill the beans that I've seen before include "To sing" , "Give away secrets" , "Blurt out secret" , "Embarrassingly reveal a secret" , "Disclose, confess" .)