This is a common embellishment for back ochos and takes a little practice to work up the speed to do it but once you do you'll find lots of places to fit it in. During back ochos, beat your free foot in front as it passes the other on the "&" count (halfway through the beat), before stepping behind into the next step. (You should feel the achilles tendon at the back of the free leg hit the lower part of the shin of the standing leg, just above the ankle.) Try not to let your legs turn-out as you do this and make sure the free foot does not sickle or flop - either point your foot or flex it but make sure it is energized.

The leader will not give you extra time to do this, he will continue moving forward so you have to be fast to get your foot in front of your standing leg and then back out again without tripping yourself up. Think of the accent being 'out!' away from the leg, instead of 'in!' towards yourself. Be careful not to stab yourself with your heel or kick the leader.

Eventually try to get it so the beating movement only happens from the knee down of the free leg and cannot be felt in the upper body. Try not to tense your muscles as you do it and remember to breathe!

At first you may find it easier to beat the left foot in front of the right as you have slightly more space on the open side of the embrace. Once you get good at it try not to beat on every step, but only when you hear an accent in the music.

Variations

-You can also do this movement very slowly when the leader pauses between ochos, by dragging the free foot in front of the other langorously.
-Find other places to do the beat besides during ochos, such as during a rock-step, before going forward outside the leader (as in an ocho cortado or back corrida), before stepping forward over a leaders leg during a parada, or during a turn after any back crossing step.
-Make the beat really sharp, hitting hard against your own leg, with the beating foot flexed.
-Make the beat a quick and light flick, with your foot pointed.
-As you beat with your foot, also raise the thigh up so the foot travels up along the standing leg as it comes in. You could raise the thigh just a little, or a lot so it's almost like a front boleo, depending on the space you have.
-Try, if you are really fast, to do 2 beats!

Exercises for Home

-Practice walking backward, doing a beat with each step. Try not to let the beat slow you down or make the step become jerky. Remember to get your leg all the way stretched back and straight into the next step after beating. Try all the tap variations above as you walk.
-Now try the beat with back ochos, both with pivot and without. Hold onto a wall for balance if need be.

Exercises for the Bus Stop or Grocery Line

-Stand on one leg and beat the free foot in front of the other repeatedly, making sure the leg is moving only from the knee down. This is great for building your quads! See how fast you can go. Try with the foot pointed, and then flexed.