According to John Dunning—head coach at Stanford University—one of the keys to team defense is individual defense. Being able to read the ball is a crucial component of individual defense.
Dunning teaches reading in two parts: the first read looks at the angle the attacker faces, while the second read focuses on what the attacker does as they prepare to hit.
As players develop their reading skills, he emphasizes things like eye work, defensive positioning and layering. To find out more about those key terms and see him work on their first and second reads, check out this video.