...performs when high and behaves badly (4,2)
I believe the answer is:
acts up
'behaves badly' is the definition.
(acting up is a kind of behaving badly)
'performs when high' is the wordplay.
'performs when' becomes 'acts' (acting is a kind of performing. I am not sure about the 'when' bit.).
'high' becomes 'up' (associated in meaning).
'acts'+'up'='ACTS UP'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for acts up that I've seen before include "Causes trouble or misbehaves" , "Behaves badly (colloq.)" , "Behaves in a troublesome way" , "Malfunctions" , "Carries on" .)