Mints unwrapped before performance is complete (6)
I believe the answer is:
intact
'is complete' is the definition.
(intact can mean complete or undamaged)
'mints unwrapped before performance' is the wordplay.
'unwrapped' means to look at the middle letters (the letters which wrap the word are removed).
'before' means one lot of letters go next to another.
'performance' becomes 'act' (act is a kind of performance).
The central letters of 'mints' are 'int'.
'int'+'act'='INTACT'
(Other definitions for intact that I've seen before include "Entire, undamaged" , "Undamaged, not broken" , "Entire and whole" , "Not damaged or missing a part" , "Entire and complete" .)