The outside barrier eliminates "casting". It keeps you form swinging "long" and helps you "keep the hands inside the ball". If the bat or arms are extended prematurely the bat head will slap the flexible upright barrier post. For years coaches have set a tee adjacent to a fence or screen to force hitters to compact their swing. The outside barrier does the same thing except it is a lot more effective. It rotates around the tee to accommodate LH or RH hitters and it moves along with the forward arm to help you keep the hands "tight" when you are working on inside and outside pitch locations. With the outside barrier you are forced to rotate the hips and torso and extend the hands only at the point of contact. It produces a "quick" bat and more power as well.