glass said:
How does it all work? What do the quarterback and the linebacker and (whatever the other positions are called) actually do?
Some other answers / elaborations....
Football positions have become pretty specialized. Particularly once you get to the college or professional game, a player will either play on offense or defense; you do occasionally get someone who's such an exceptional athlete that he can excel at positions on both sides, but that's a rarety.
The typical offensive positions are:
Center. The middle of the five offensive lineman, he begins each play by "snapping" or "hiking" the ball to the quarterback.
Guards. The two linemen on either side of the center.
Tackles. The two linemen on either side of the guards.
When the offense is lined up, going from left to right, you see them lined up as Left Tackle / Left Guard / Center / Right Guard / Right Tackle.
Offensive linemen's primary jobs are to block the defensive players, to keep them away from whoever has the ball. On a running play, they will often move past the line of scrimmage (the line that the ball starts on) to try and move the defenders out of the way of the ballcarrier; on a passing play, they usually backpedal, following the quarterback as he drops back to pass. They tend to be among the biggest players on the field.
Wide receivers. These are, usually, the primary targets for passes. Technically, there are two different wide receiver positions; a "split end" lines up on the line of scrimmage (though, usually, some distance away from the interior linemen); a "flanker" lines up a yard or so behind the line of scrimmage.
On most plays, the wide receivers will run downfield, running very precise patterns ("pass patterns"). Most wide receivers are fast runners; those who don't have very good hands don't last very long.
Tight end. The tight end is sort of a hybrid between a tackle and a wide receiver. He lines up on the line of scrimmage, right next to the tackle, on the opposite side of the ball from where the split end lines up (and now you know why they call them "tight end" and "split end").
On running plays, the tight end usually blocks, like a lineman; on passing plays, he usually runs a pass pattern. Some tight ends are better at one job than the other; most of the truly great ones excel at both. Due to the blocking requirements of the position, they tend to be bigger than wide receivers (and often, not as fast).
Quarterback. Pretty much every play goes through the quarterback; many believe that he's the single most important player on a team. On running plays, the quarterback takes the snap, and hands it off to one of the running backs (or, may run it himself); on passing plays, he backpedals a bit (to give himself some time), and then throws the ball to a receiver.
Quarterbacks need to be able to quickly analyze what the defense is doing, and adjust what they're doing in reaction. They need a strong, accurate passing arm, and, usually, some degree of mobility to be able to get away from defenders (though there have been a few quarterbacks who have been very successful despite being very slow). Many coaches believe that a quarterback needs to be fairly tall (or, at least not be short), in order to see over the other players; whether this is the case or not, there have been fairly few successful pro quarterbacks shorter than about 6' tall (Doug Flutie and Eddie LeBaron being two notable exceptions).
Halfback. On most teams, the halfback (one of the two running backs) is the primary person responsible for running the ball. Most halfbacks are very fast, with good hands; they must also be durable, because they can take a real pounding. They don't necessarily have to be very big (some of the great ones have been under 6' tall), but being strong is a definite advantage. Some halfbacks are also good receivers.
Fullback. A generation ago, the fullback was just the bigger and stronger of the two running backs, and was called on to carry the ball when the team only needed a few yards. At least in pro football, most fullbacks now are expected to primarly be blockers, leading the way for the halfback on running plays, and blocking for the quarterback on passing plays. Many fullbacks rarely, if ever, carry the ball anymore, though some are often called on to catch passes.
Those are the "standard" positions. Some teams run offenses that change some of these positions entirely....for example, some teams run an "H-back" formation, which replaces the fullback with, essentially, a second tight end. Back in the 80s and early 90s, some teams experimented with the "Run & Shoot" offense, a pass-oriented system that replaced the tight end and fullback with 2 additional wide receivers.
Even if a team runs a "standard" offense most of the time, they may make situational changes, like replacing one running back with an extra wide receiver on a "passing down" (typically 3rd down, with 5 or more yards needed for a first down).
And, for the defense...
There are three basic defensive areas: linemen, linebackers, and defensive backs.
Defensive tackles. They play near the center of the line. If a team plays a "3-4" defense, they only use 3 defensive linemen, and thus use only 1 defensive tackle (who may, then, also be called the "nose tackle"). In a "4-3" defense, the team uses two defensive tackles.
Defensive tackles are often the very biggest players on the field, and they're primarly there to stuff the inside of the line and stop the run (though some are good at rushing the passer, as well). If a team plays a 3-4, the nose tackle usually lines up directly opposite the offensive center; in a 4-3 defense, the defensive tackles usually line up directly opposite the offensive guards.
Defensive ends. They play at the "ends" of the line (hence the name). They're often not quite as big as the tackles, as they are often the primary pass-rushers (pursuing the quarterback on pass plays), though they also need to be able to stop the run. The defensive ends typically line up opposite the offensive tackles.
Linebackers usually play a yard or two off the line of scrimmage, though some may move around quite a bit. On running plays, they move to stop the runner; on passing plays, they may "blitz" (rush the passer), or stay back and cover receivers.
Middle linebacker. They often play a big role in stopping runs "up the middle", though they also need to be athletic enough to rush the passer or cover receivers coming over the middle.
If a team plays a 4-3 defense, the middle linebacker lines up between (but slightly back from) the two defensive tackles. If a team plays a 3-4 defense, they use two middle linebackers (technically called "inside linebackers"); they usually line up between the nose tackle and the defense ends.
Middle linebackers are often some of the most feared players...famous players like Brian Urlacher, Ray Lewis, Mike Singletary, Jack Lambert, Dick Butkus, Ray Nitschke, and Sam Huff are/were all middle linebackers.
Outside linebackers. Like middle linebackers, have a lot of roles to play, being asked to stop the run, rush the passer, and cover receivers. Many outside linebackers are good pass-rushers. The outside linebackers typically line up "outside" of the defensive ends.
Cornerbacks and safeties. These are the four defensive backs (also known as the "secondary"). Their primary role is to cover receivers (particularly the wide receivers and tight ends) as they run their pass patterns; they try to keep the quarterback from being able to complete his passes. They also have a secondary role of stopping runners, if they make it past the linemen and linebackers, and some defensive backs may occasionally even rush the passer.
Traditionally, the left cornerback and right cornerback were responsible for covering the wide receivers; the strong safety covered the tight end, and the free safety often followed the ball, or played "centerfield" (yes, that's a baseball term) on pass plays. Most pro and college teams now play some sort of zone defense, and so those clear definitions of "who covers whom" don't always fit.
That's defense...now for special teams.
Kicker. The kicker's job is placekicking (a kick that can score points if it goes through the goalposts).
If a team is fairly close to the other team's end zone, but their drive stalls (usually, if it's 4th down), they can elect to try a field goal. If the kicker can kick the ball through the uprights, this scores 3 points. Most pro kickers are fairly accurate out to about 50 yards; a few kickers can kick field goals of 60 yards or a bit more (though with diminishing accuracy).
In addition, when a team scores a touchdown, they are allowed to try a "conversion" or "point after touchdown". This is just like a field goal, only it's done from very close to the end zone (usually the two-yard-line) for an addtional point.
(In most leagues, a team can also try what's called a "two-point conversion"; this isn't a kick at all, but a regular offensive play, usually also from the two-yard-line. If this gets into the end zone, it counts for 2 points; however, as it's usually a lower-percentage play than a kick, most teams don't do this unless that additional point really matters.)
Finally, a kicker is responsible for kickoffs...this is how the ball is put into play after a team scores, or at the beginnng of each half. The kicker kicks the ball from a tee, trying to get it as far downfield as he can; when the other team catches the ball, they take possession, and run it back the other way as far as they can.
Up until the 1960s, all kickers were "toe-style" kickers...they wore a square-toed shoe on their kicking foot, and kicked it straight-on, sort of like a pendulum. Over the course of the 1960s and 1970s, "soccer-style" kickers, who kick using their instep, and approach the ball at an angle, like a soccer player became the norm. The first soccer-style kickers in pro football were often European or Latin, and often knew little about the rest of the game, but as more Americans grew up playing soccer (and kicking the ball that way), that's changed, and now most kickers are Americans. (I don't think there's been a "toe-style" kicker in the NFL in 20 years or so.)
Punter. The punter's job is to give the ball over to the other team. As noted by others, the offense has 4 plays (3 in Canada) in which they need to gain 10 yards. If they fail to do this, the other team gets possession of the ball at that point. If, on 4th down, the offense is too far away from the end zone to have a reasonable chance of trying a field goal, they will usually punt the ball. A punt looks a lot like the sort of kick that a soccer goalie would use to clear the ball away from the goal (he takes the ball, drops it, and kicks it while it's still in the air), and it's returned much like a kickoff is.
Particularly in pro football, kickers and punters are often seen as not being "real" football players, probably because they tend to be smaller (and a few of them have had rather portly builds). But, most of them are very athletic, if specialized, and many of them played "real" positions as well in high school, if not in college.
Phew. That was longer than I thought it would be.
