Run in one direction, then tap and hold backward to turn sharply, sliding with inertia briefly before reversing course.
Pivoting isn’t just cosmetic. During a pivot, a fighter turns around and scampers against their own momentum. This is still moving forward relative to the original running direction, so jumping or attacking backturned from this state can be powerful on purpose. Many fighters have different ground pokes that are useful to aim backward, including many up tilts and down smashes, and this trick allows their aggressive use from a backward slide. Similarly, the reverse air rush technique enables aggressive backturned aerial movement, starting out running at an intended target, pivoting, then hopping at foes with back air.