Misbehave when put roughly in reverse (3,2)
I believe the answer is:
act up
'misbehave' is the definition.
(acting up is a kind of misbehaving)
'put roughly in reverse' is the wordplay.
'roughly' becomes 'ca' (abbreviation for circa).
'in reverse' is a reversal indicator.
'put'+'ca'='putca'
'putca' written backwards gives 'ACT UP'.
'when' acts as a link.
(Other definitions for act up that I've seen before include "Misbehave - carry on" , "Behave badly, cause trouble - like thespian?" , "Behave badly (colloq.)" , "Mess about" , "Behave badly, give trouble" .)