go off the reservation

The Indian may go off the reservation, he can steal from the whites and run back to the reservation with impunity.

This hand was ready to give the works to any physician, a member of the Medical Association in good standing, who'd go off the reservation by daring to serve a medical co-operative on a full-time salary.

When the Russians do go off the reservation, as they did early in April 1965, their object is not to challenge the Western allies of yesteryear, the United States, Britain, and France, but to impress upon West Germany their support for East Germany and its claim to West Berlin.