The basic idea for sacada is the interruption, which is preventing the other dancer to collect the feet because of the sacada foot, which is blocking the way. An educated, skilled partner's foot is taking a detour around that foot before completing the step. According to David a slight contact with the two legs makes the sacada possible.
As my follower steps, she creates a space between her feet that starts small, widens to about 50 cm (more or less), then closes as she collects her legs. This is the gap into which I must intrude my leg. In the journey her leg will take, I want it to encounter my leg softly and be deflected, maybe not much, but enough to feel different to her and look different to an observer. (p. 165)The initial instruction he got was to place the sacada foot near the partner's departing foot and directly change his own weight on that foot. The problem was that the sacada space was hard to find, he bend down for a better look and destroyed the balance. He was anxious too of hitting/injuring the delicate foot in an open shoe.
The sacadas started to flow when he understood the timing and start to place the sacada foot as soon as the follower had landed on her side step. When the follower is stepping evenly the sacada space will open and close predictably and the leader can feel the actual state of a step by feeling it through her upper body. With other words you feel from her upper body where and when a possibly gap for a sacada is.
The outcome of intrusion can be a smaller detour, a bigger planeo or a gancho. All this depends more or less on following choices:
Placement of sacada btwn the feet; near the standing (Ga) or departing feet (Sa)
Point of contact; higher on the leg (Ga) or lower on the leg (Sa)
Form of leader leg; like S with the heel up (Ga) or more stright (Sa)
The leader thigh: more horizontal (Ga) or more vertical (Sa)
Weight recommendations for sacada foot: less weight gives more soft leg, possibility to lift the heel (Ga) or more weight (Sa)
The dynamics of this movement is created by the rotation when the follower's hips are moved away to give space for leader to take that spot. Here you have David's description:
The rotation is essential not just to maintain the frame, as usual, but also to provide the impetus for the sacada. This impetus means that my follower's left leg quite naturally swings out, away from my leg, almost as if it has been kicked away. (p. 168)
According to David the follower (receiving partner) can facilitate the sacada by stepping evenly and predictably. If she is well balanced on her weight-bearing leg and permitting her free leg full freedom of movement will make it all easier. During the dynamic part of movement the leg should swing away from the hip and the movement should in the whole feel quite natural.
Turner, D. (2006). A Passion for TANGO, 164 -169
For me the idea of a line between the receivers feet and the sacadas intention to bend that line became the most valuable idea during the reading.