Section 42 of the Criminal Procedure Act 51 of 1977 allows a Private Person to make an arrest in the following circumstances:

A Private Person can arrest any person without a warrant –

• who commits or attempt to commit an offence in his presence or whom he reasonably suspects of having committed an offence as referred to in Schedule 1;
• whom he reasonably believes to have committed any offence and to be escaping from and to be freshly pursued by a person whom such private person reasonably believes to have authority to arrest that person for that offence;
• whom he is by any law authorized to arrest without a warrant in respect of any offence specified in law
• whom he sees engaged in an affray