This drill from Kevin Hambly has one player on each side of the net. One side has a setter and the other side has a player that chooses a direction to run (left or right) immediately before the setter contacts the ball.
The purpose of the drill is to increase setter awareness and decision-making, based on what is happening on the other side of the net. The setter should try to read the direction the defender is moving and set the ball in the opposite direction.
As the drill progresses, Hambly has the defender move later and later, making the window of time that the setter can read shorter and shorter.