This is achieved by crossing your rear leg past the back of your front leg. Legs cross at the thighs, not the knees. Done properly this step gives you the greatest gain in ground. The shuffle or step-drag should be reduced or eliminated for multiple combat. By stepping your front leg out and sliding your rear leg forward you don't gain much ground and your step is very predictable.
Predictability is something to avoid.
The first step in a step-drag is also a negative time frame. Finally, there's moving backwards. The only reason to step backwards is to attack. Moving backwards to retreat allows your attackers to triangulate on you. Every attacker will converge on you at about the same time.