This is KlickSpeed.

KlickSpeed™ is a backside arm mechanics training device. It was invented by former track & field coach, David Case, as a solution to an issue he encountered frequently over years of training athletes: bad backside arm mechanics.

In practically all sports, bad arm mechanics leads to instability, inefficiency, and inability to reach top sprint speed and/or distance endurance. Good arm mechanics can occasionally be taught through coaching alone, but often times bad mechanics are simply too hard of a habit to break. KlickSpeed™ offers a solution to this problem—one without a coach watching every swing of the arm.

With good backside arm mechanics, you get one step closer to: