In a mugger’s choke, two-man attack teams walk up behind a person or a couple. One suddenly grabs a person in a rear naked choke, pushes the person’s opposite elbow forward so the person cannot jab it backward, and then quickly starts pulling the person backward so the person is leaning backward and off balance. From behind, the other attacker quickly goes though the person’s pockets, taking anything valuable. Then, the first attacker drops the person on his or her butt and runs. It is all done very quickly and smoothly from behind. The victim is not injured and he or she never sees the attacker. Many times the person’s partner or bystanders do not even see the attack happen, yet alone see the attackers.
Your case of being held in a rear naked choke and hammerlock is similar to the mugger’s choke. Some defenses to use are to turn your head into the crook of the choking arm and pull down on the forearm to release pressure, bite the arm, and stomp the attacker’s toes or kick the shins. A backward head butt is possible, but if the assailant's head is too close, the butt may be ineffective. If you are falling backward, launch yourself backward explosively with your legs to knock the assailant off balance. You may land atop the assailant and injure him or her. If not, you are at least prepared for the fall and the assailant will be caught unprepared. If you are falling forward, pull forward, and tuck and roll, dragging the attacker with you.