Action in open court is disturbed (11)
I believe the answer is:
prosecution
'action' is the definition.
(thesaurus)
'open court is disturbed' is the wordplay.
'disturbed' indicates an anagram.
'open'+'court'+'is'='opencourtis'
'opencourtis' anagrammed gives 'PROSECUTION'.
'in' acts as a link.
(Other definitions for prosecution that I've seen before include "Lawyers acting for the crown" , "Bringing of criminal action" , "one side of suit" , "Legal proceedings" , "Accusation of guilt in court" .)