Here are several snap down examples some better than others.  Back handsprings have two flying phases  one from feet to hands and the second turning from hands to feet.  Snap downs help gymnast to understand the second flying phase.  She could open the shoulders more to begin the snap down.  In this example notice a much better shoulder opening to begin the snap down.  /4th clip/ Better shoulder opening.  /6thclip/  After Gymnasts can snap down safely from folded mats they can try from spring boards.  The extra bounciness facilitates to train the deep hollow turn over without having to pike down. This is an incorrect  snap down with an excessive pike. This gymnast shows a better turnover with a deep hollow position.