The play of the linebacker position has captured the eye of NFL fans since the first days of the game. Even today, almost 100 years later, the position remains one of the more exciting positions in the game, but how many fans truly understand the differences between the three or four linebackers on the field at a time?

Football fans are smart individuals, but there is more to the game than the average fans sees on every down. In the "Football 101" series, you'll get a look at the assignments, plays and schemes that make the game of football so diverse, complicated and intricate. Today we'll take a look at the what the differences are between a weak-side, strong-side and middle linebacker in basic NFL schemes.

4-3 Defense

In a 4-3 defense there are three linebackers on the field in a base set. These are broken down into a weak-side, strong-side and middle linebacker. Where they line up on the field is based on which position they play.

The different linebacker positions are broken down by the alignment of the offense.

Our strong-side linebacker (SLB) will line up across from the side of the offense—starting at the center—which has the most players on that side. If the number is equal, we count men on the line of scrimmage. As a general rule, the SLB will line up across from the tight end if each side has the same number of personnel.

Just as the strong-side linebacker goes on the side with the most players, the weak-side linebacker (WLB) goes on the side with the fewest. And as you may have guessed, the middle linebacker (MLB) goes in the middle of the two.

The assignments of the players may vary within each scheme, but it is most common for the "Sam" linebacker (strong-side) to be a better pass-rusher, due to his alignment most often across from the tight end. This makes our "Will" (weak-side) linebacker more of a coverage linebacker.

3-4 Defense

Like the 4-3 defense, in a 3-4 the alignment of the four linebackers is based on their weak- or strong- side designation—at least in a base defense.

The 3-4 defense's principles are much like a basic 4-3, only there are two middle linebackers as opposed to one.

The SLB is still a pass-rusher first and foremost, but in a 3-4 defense the WLB is also a pass-rusher in most schemes, although it is very common for the WLB to be used in pass coverage as well. Teams like the San Francisco 49ers are bending that philosophy by utilizing both outside linebackers as heavy pass-rushers.

It's easy to think of the 3-4 defense this way: The outside linebackers are blitzers; the inside linebackers are "jack-of-all-trades" men who must stop the run, rush the passer and drop back in pass coverage.

You will also see middle linebackers labeled as "Mike" and "Ted." The "Mike" linebacker is a classic middle linebacker, but the "Ted" 'backer fills a role much like a fullback. His job is to step up first and take on blockers, freeing a path for the "Mike" 'backer to make tackles.

There are also teams running a 3-4 defense, like the 2011 Green Bay Packers, who do not choose to designate between weak and strong side, instead going with a simple "left outside linebacker" and "right outside linebacker" alignment.

Here's a very quick look at how you can remember each position's most common use:

Sam—Better tackler. More commonly used as a pass-rusher. Tight end side.

Will—Fastest of the three. Generally better in coverage. Slot receiver side.

Mike—Captain of the defense. Makes play calls. Must be able to tackle, blitz and cover.

As with any defense in the NFL today, coordinators are constantly changing the rules in an effort to stay one step ahead of offenses. These are meant to give readers a basic understanding of formations and terminology and are not intended to be thought of as the only way to run a defense.

Have a topic you want to see covered in the Football 101 series? Let me know on Twitter @nfldraftscout.