This is an excerpt from Complete Book of Throws by Jay Silvester.
In discus throwing, the term reverse derives from the action that naturally occurs for most discus throwers when using the side arm sling. The feet reverse their delivery positions. For example, a right-handed thrower would deliver the discus with the left foot forward and the right foot back. The violence of the throw (lifting and driving the right hip, shoulder, and arm into the throw) usually results in the right side being driven to the front while the left side rotates to the rear—thus the term reversing, which is short for reversing the positions of the feet.
To properly orient a thrower or coach in the circle, two things are necessary:
1. Clock system imposed on the circle with 6 o'clock as the direction of the throw (figure 4.4)
2. Line bisecting the circle from 12 to 6 o'clock
To be in the proper starting stance, face 180 degrees away from the throwing direction; your feet should be wider than shoulder width (figure 4.5). Your left foot should be either on the line or slightly left toward 11 o'clock. All phases of the throw are important, but I consider the phases from the start through the end of the first single-support phase as the most crucial. Double support means two feet on the ground. Single support refers to only one foot on the ground. Your feet should be wider than shoulder width for stability and also for the potential to move from the right to the left foot to allow somewhat of a running start. By running start I'm referring to the body mass moving over a range (width of stance) to develop momentum before moving across the circle.