Misbehave in performance, getting excited (4,2)
I believe the answer is:
play up
'misbehave' is the definition.
(I've seen this before)
'performance getting excited' is the wordplay.
'performance' becomes 'play' (I have seen 'Theatrical performance ' mean 'play' so perhaps 'performance' could also mean 'play'**).
'getting' means one lot of letters go next to another.
'excited' becomes 'up'.
'play'+'up'='PLAY UP'
'in' acts as a link.
(Other definitions for play up that I've seen before include "(Equipment) start malfunctioning" , "Behave uncooperatively" , "Be awkward" , "stress" , "Be painful - misbehave" .)