The crossing needs a clear path in front of the standing foot
When crossing to the left in the Viennese Waltz, the left foot should not simply land beside the right. On count three, it moves in front of the right foot. This crossing belongs to the forward-moving half of the turn to the left, not to every Waltz measure. The person dancing backward therefore does not take the same crossing path at the same time.
To correct it, separate two tasks: the path of the free foot and the weight transfer that follows. If the left foot is still bearing weight, you cannot bring it in freely. If its shoe edge meets the right shoe before passing its front, a bottleneck forms. Pulling harder on the leg will not create more space there. Instead, it can drag the standing foot along.
So the isolated exercise starts in your familiar position after step two. Keep that alignment instead of inventing a new ending position. You are looking for a narrow passage without contact, not the deepest possible cross. The principle of separating tasks first also helps with coordinating arms and legs. For now, keep your arms still so you can feel the path of the foot. The full turn and its amount of rotation are not rebuilt here.


