This throw is used against a straight punch.
As your attacker throw the punch, block the strike with a basic inside forearm block and step forward and to the left with your left foot. Your foot should be next to your attackers right foot.
Use a ridgehand strike to your attackers main artery in their neck. A powerful strike here will cause them to nearly pass-out.
Now push on your attackers left shoulder to take them off balance. This will make the throw much easier.
Take your right leg behind your attackers right leg.
Sweep your attackers right leg forward with your right leg. Once they are on the floor you may finish with a strike or arm-lock.