This is an excellent drill tha involves several aspects on coming out of the back of the ring in rotational throwing.  After your athlete is proficient at 360 degree turns the unwinding to a loaded left leg this drill is the next progression.  They should focus on all the aspects of the 360 degre turn along with trying to sink on the left leg.  I use the cue "try to dip your left knee to the ring". This gets the athlete to really load the left leg as they prepare for the drive out of the back. You as a coach are looking for the proper balance of the athlete out of the back. You should see a straight vertical line that extends from the athletes knee up to ther left shoulder.  This is an indication that they are on balance.  If you want you can add to this by having the athlete sweep their right leg through past the left leg, leading with the inner thigh.