Police were called after reports of a man seen acting suspiciously outside The Castle Theatre in Wellingborough.
The man, who was wearing a black hoodie with the hood up and black leather gloves, was seen acting suspiciously while a rehearsal was taking place.
He was challenged by a woman who shouted at him and he then ran off.
Police are appealing for this witness to come forward to help them with their investigation into this incident, which took place between 8pm and 8.40pm on Thursday, July 3.
Witnesses or anyone with information about it is asked to contact police on 101 or Crimestoppers anonymously on 0800 555111.