Quickturning is one of the most basic and important techniques in JSRF speedrunning. It is performed by skidding, then dragging the control stick to the character's left. This cancels the animation before your speed drops, allowing you to skate out of the skid at full speed. Although quickturning can be performed with any character, it is easier for characters with high cornering. You cannot quickturn to the right.
Quickturning is also possible while skating backwards. Reverse quickturning usually results in much sharper turns - quickturning a full 180 degrees is much easier when skating backwards.