This is an excerpt from Football Skills & Drills - 2nd Edition by Thomas Bass.
Playing zone pass defense is the opposite of playing man-to-man pass defense. In man-to-man coverage, the focus is on the running back. The linebacker allows the receiver whom he is covering to tell him where to go by running a route, and the linebacker runs all over the field to cover the receiver for the entire length of the play. In zone defense, the linebacker is assigned to a specific area of the field. He reacts to any pass thrown in that area regardless of who is trying to make the catch. When playing zone defense, the linebacker must recognize the pass play, go immediately to his zone, get as deep in his zone as he can before the quarterback sets to throw, focus on the quarterback and the ball, and react to the pass. The ball directs the linebacker to the receiver.
First, the linebacker should learn the zones that he will cover. The coach should outline the names and zones that will be used in the defense. On each zone pass defense, the linebacker is assigned one of the zones. Figure 8.16 shows one way to divide the medium zones on the field.
The technique that the linebacker uses to drop into his zone depends on how wide he has to go from his original position to get into the zone. The wider he has to go, the more he will have to sprint. When he sprints, the linebacker rolls over the foot in the direction that he needs to go and runs as fast as he can to his area. He should constantly look back over his shoulder to the quarterback.
After he reaches his zone, he swings his inside leg around and begins to backpedal. As he starts to backpedal, he focuses on the quarterback. When he sees that the quarterback is ready to throw, he stops his backpedal but keeps running in place, moving his feet in short, choppy steps. He prepares to move to either his right or his left when he sees the quarterback start to throw. The linebacker breaks to the ball by rolling over the foot in the direction that he needs to go.
One challenge that a linebacker faces when playing zone defense is keeping his eyes on the quarterback and not looking at a receiver running into his zone. The linebacker may want to come up to cover the receiver before the ball is thrown, but he must resist this temptation. He must practice going to his zone, looking at the quarterback, backpedaling, and then reacting to the right or left based on the throw. He should let the quarterback and the ball take him to the receiver. Focusing on the quarterback and the ball gives him a great chance to make an interception.
When playing zone pass coverage, the reaction of the linebackers to a draw or screen pass will be different in that they must first concentrate on moving to their assigned zones rather than focus on one offensive player.
The linebacker will likely be moving away from the line of scrimmage when he recognizes that the offense is running a draw or screen pass play. An inside linebacker can help defeat the draw play if he backpedals for the first few steps until the quarterback is past the running back and not in position to hand him the ball. With this technique, the linebacker can keep his shoulders square to the line of scrimmage and quickly come up if he sees the draw play being run.
To react to the screen pass from zone pass coverage, the linebacker usually has to avoid the offensive blocker coming from the inside. Because of his depth off the line, the linebacker will not normally reach the running back until after the back has made the reception.