Region: General | Usage example: He went behind her back to change the agreement.

Go behind someone’s back

Meaning

Act secretly, especially against someone's trust.

Used to criticize sneaky or disrespectful behavior.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

Medieval court imagery of acts performed without the subject’s knowledge.

Used since at least the 17th century in discussions about betrayal.