This is an excerpt from Complete Linebacking-2nd Edition by Lou Tepper.
A linebacker or coach should be able to recognize styles of play similar to his own. To accomplish this task we need a common language to describe the techniques. We use numbers for techniques in which linebackers play unprotected over blockers at the line of scrimmage. We use names for techniques in which a linebacker is protected by a fellow defender from the potential blocker directly over him.
Numbered techniques have two digits when the linebacker plays off the line of scrimmage. The first digit refers to his frontside responsibility (see figure 10.1).
A linebacker off the line of scrimmage has a double-digit technique beginning with a 3 if he is responsible for the frontside guard-tackle gap or a 5 if accountable for the tackle-end gap.
His second digit has to do with his backside movement. When the linebacker is required to “fast flow,” or run, on action away from him, he is given the second digit of 1. Usually a fast-flow linebacker must fill an unattended backside gap as in figure 10.2.
The 31 technique linebacker has the 3 gap with flow to him and the away 1 gap with flow away.
When the linebacker’s backside obligation is to shuffle with no particular gap responsibility away from him, he is a single-gap player. His backside digit, in our system, is a 2. Figure 10.3 shows a 32 technique player. Other defenders are responsible for all backside gaps.
Numbered techniques with single digits refer to outside linebackers on the line of scrimmage who are liable for that gap only, on flow to or flow away (see figure 10.4).
An outside linebacker could be responsible on the line of scrimmage for the 5 gap (tackle–tight end gap), the 7 gap (referred to as the alley), or contain (referred to as a 9 technique).
We use names for linebacker techniques that provide some protection for the linebacker. Figure 10.5 shows a nest technique. We call it a nest because the linebacker sits in a protected cradle that can be designed for weaker or younger players (see figure 10.5).