The security guard had a right to make a citizen's arrest since she witnessed a crime trespassing. She was justified in handcuffing the woman. She can enforce laws if she witnesses the crime and can use handcuff to arrest someone especially someone who just assaulted her. She is not obligated to contact authorities and neither are you. If you witness a crime you can act and make a citizen's arrest and then call the authorities after within a reasonable time.
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