Use a sniper rifle with a silencer to avoid attracting more Zeds while you are dealing with the Juggernaut. Up to ten shots to the head may be required, depending on the rifle used. With good aim and enough distance, you should be able to kill the Juggernaut without it charging. Run the Juggernaut over with a car after back into it at full speed. This will heavily damage your car, especially the tires, but will also knock it over. Quickly accelerate to get decent speed and run it over before it manages to get up again. If done correctly, it will kill the Juggernaut. If it gets up before this happens, hit him anyway and total your car. Quickly find another vehicle to hit him a third time for the kill.