To perform on stage, I have to be brisk (6)
I believe the answer is:
active
'be brisk' is the definition.
(thesaurus)
'to perform on stage i have' is the wordplay.
'to perform on stage' becomes 'act' (I've seen this in another clue).
'i have' becomes 'I've' (contraction of 'I have').
'act'+'ive'='ACTIVE'
'to' is the link.
(Other definitions for active that I've seen before include "Not extinct (of volcano)" , "Mobile" , "Keeping busy, not lazy" , "kind of voice" , "Busy, energetic" .)