The stepover move is a very complex move that a pitcher does with his back foot and landing foot that helps keep weight back longer and exaggerates weight transfer that translates into velocity. The longer a pitcher can keep their front side leg up high off the ground while keeping their weight on their back leg the longer their stride will be more powerful you will come down and land. The more power you can get into landing the faster you will rotate.
When lifting your leg when you come down you want to tilt your shoulders back towards 2nd base. The tilting will help keep weight back and create leverage of the core that you can use into landing and delivery of the baseball.
Examples of pitchers who do this are Tim Lincecum and Jake Arrieta.