Simply put:
The pitch starts when the hands separate.
The pitcher may take a backswing before beginning the forward windmill (assuming windmill motion here).
Once the forward motion starts, the pitcher may not stop or reverse the motion prior to delivery of the pitch.
The pitcher must not throw sidearm.
The pitcher must not make another revolution of the arm after release.
The pitcher must not make two complete revolutions with the arm before release.
This part of the rule is only about 1 page long, but I'd rather not type the whole thing.
