Pitching mechanics from the windup position

I am currently taking classes to become a high school umpire. The rule for pitching from a windup states that a pitcher may only deliver a pitch,or step backward off the pitchers plate with his pivot foot first. In the case book for nfhs in presents a situation, from the windup position F1 steps onto the pitchers plate with both hands together. As he moves his non-pivot leg behind the pitchers plate,he completly stops his motion. The ruling on this would be a balk if there were any runners on base. This is confusing to me. What is the rule for federation baseball pivot foot or non-pivot foot stepping back first?

Sprinkler, I can only speak from the point of view of the major league rule covering this, because when I pitched we went by that. Let me quote Rule 8.01 on this: "The pitcher shall stand facing the batter, his entire pivot foot, or in front of and touching and not off the end of the pitcher’s plate and the other foot free. From this position (full windup), any natural movement associated with his delivery of the ball to the batter commits him to the pitch without interruption or alteration. He shall not raise either foot from the ground, except that in his actual delivery of the ball to the batter he may take one step forward and one step backward with his free foot."
And Rule 8.05, which deals with balks, states at the beginning that if there is a runner, or runners, on base, it is a balk if the pitcher, while on the rubber, fails to complete his delivery to the plate. Of course, he’s working from the stretch, or the set position in this instance. But we’re talking full windup here. Example—and this has happened: the pitcher is on the rubber, starts his windup, and drops the ball! It just squirts out of his hand and drops to the ground with a resounding “plop”. Well, with no one on base, it’s not a balk. The umpire can call it a ball—or he might not do anything, it was just an accident.
Of course, when the bases are loaded the pitcher can go to the full windup if he wishes. The one advantage there is that the runner on third will have to think twice before attempting to steal home, or the manager will have to think twice before attempting a squeeze play, because in either case the pitcher is staring him in the face and could easily set up a play in which that runner is cut down at the plate. But it doesn’t always work. Here’s an example, from September 17, 1951. It was the bottom of the ninth inning with the score tied 1-1 and one out. Phil Rizzuto was at bat with one strike on him. And the suicide squeeze was on, with no one except Rizzuto and Joe DiMaggio knowing about it. Rizzuto bunted—a beautiful dead-fish bunt between the mound and first base, with no one able to make a play on it, and DiMaggio, who could have crawled to home plate, took off from third like a shot and scored standing up. Game over; Yanks won, 2-1.
Anyway, that’s the skinny on full windup. Maybe the rules are different in high school or other non-professional baseball, but the major league way is how I know it. 8)