Ballad none performed, because it's toxic (10)
I believe the answer is:
belladonna
'because it's toxic' is the definition.
I can't tell whether this defines the answer.
'ballad none performed' is the wordplay.
'performed' indicates anagramming the letters.
'ballad'+'none'='balladnone'
'balladnone' is an anagram of 'BELLADONNA'.
Can you help me to learn more?
(Other definitions for belladonna that I've seen before include "Could it poison" , "drug supplier" , "Drug made from deadly nightshade" , "Boy in Lebanon destroyed" , "brought a sparkle to the eye" .)