In the back ocho you draw the eight going backward. Learn to stay safe: backward steps, pivot, typical mistakes and clear milestones for each stage.
The honest answer first: the back ocho (ocho atrás) is the figure eight going backward: the follower walks diagonally backward and pivots on the standing leg between steps. It looks like the forward ocho in reverse but feels completely different. Behind you there are no eyes, your pelvis likes to pull back, and the torso lags behind.
That is exactly why this guide is worth it: backward steps are where beginners send the most force into the floor. In a study with 56 dancers (rhythm ballroom basics such as rumba box and cha-cha, so only a hint about partner dance in general), ground forces and loading rate were highest in inexperienced dancers, especially when stepping backward and to the left [1]. The good news: with practice it becomes soft and quiet.
The back ocho makes your tango safer. Dancers who stay calm going backward get bumped less on the floor, and leaders gain a figure that works on crowded floors too.
Realistic: you will have the rough shape after a few practice evenings. Soft and secure takes weeks (rule of thumb, not a study result).
Walk eight steps backward. The toe touches down first, then the foot rolls through, the knees stay soft. The torso stays over the pelvis. Steps are small: about one foot-length. Milestone: you walk ten steps backward without the pelvis slipping behind the shoulders. In tango walking the knees are bent more than in normal walking anyway [2]; use that as suspension.
Stand on one leg and turn chest and hips about 45 degrees. The foot follows last. Ten times per side. Milestone: the standing foot stays put, only the body turns. The feeling: you turn around a pole through the middle of your body.
Step diagonally backward right, pivot, then step diagonally backward left. On the floor the eight forms in the opposite direction to the forward ocho. Place the free foot only once the torso has already turned. Milestone: four ochos in a row without stumbling backward.
Leaders look over the follower's shoulder before each impulse and so make sure the path is free. Then they give the turn through the chest, not the arm. Followers wait until they feel the impulse. Two people with light contact align their movement without noticing; in a study with 54 participants (folk dancers, only a hint), a fingertip touch was enough for that [3]. For you: a quiet, clear impulse is enough. Milestone: followers walk backward without anxiously peeking behind.
Switch between forward ocho and back ocho without a pause. Milestone: the change sits in the beat without you stopping.
Going backward you cannot see: that is the main risk. Use the floor only when the path behind you is clear and keep your ochos small. In a survey of 218 Dutch competitive ballroom dancers (standard and Latin, so only a hint), about 81% reported at least one injury, most often in foot, ankle and lower leg [4]. Warm up, use grippy smooth soles and stop if your knee hurts. This guide explains and motivates; it does not replace supervised training.
Practise going backward along a wall with one hand lightly on the plaster. It gives your axis feedback without you holding on. If you notice the hand has to push constantly, your weight is still too far back. After the back ocho comes the giro, the turn around the leader.
The ocho atrás is the figure eight going backward in Argentine tango: the follower walks diagonally backward and pivots on the standing leg between steps. Leaders give the turn through the chest and make sure the path is free.
For most people it feels harder because you cannot see where you are going and the pelvis likes to pull back. A study also found higher ground forces in beginners for backward steps [1]. Small steps and soft knees calm it down.
Keep steps small, put the toe down first and keep the torso over the pelvis. Leaders must look behind before the impulse. Practise alone at a wall before dancing with a partner.
The basic shape often sits roughly after a few practice evenings; secure and without thinking takes weeks. That is a rule of thumb, not a study result. What matters is a quiet torso and free space behind you.
Giro in Argentine Tango: Turning Around the Leader (Molinete)