Misbehave in a court — in a court! (3,2)
I believe the answer is:
act up
'misbehave' is the definition.
(acting up is a kind of misbehaving)
'a court in a court' is the wordplay.
'court' becomes 'ct' (abbreviation used in road names).
'in a court' becomes 'up' (up before a judge).
'a'+'ct'+'up'='ACT UP'
'in' is the link.
(Other definitions for act up that I've seen before include "Behave badly, cause trouble - like thespian?" , "Become unpleasant" , "Mess about" , "Informally, behave badly or cause trouble" , "Behave badly (colloq.)" .)