You asked for it: the Association Football Tactics Thread.

[Good Intentions]

Right, here's my short description of soccer tactics. I'm going to do this by running through various tactical approaches team can and do take. It's the type of primer that I would appreciate, though it's been explained to me that I'm a little strange in how I organise information in my head. There's also the fact that I'm a late-in-life soccer fan: I didn't grow up with the game, and that might show in what follows. In any case, let's start. First I'm going to list different goalscoring approaches, then various passing styles, then positional styles, then defensive styles. With a bit of encouragement, I could then go on and talk about the different player positions and what they do. The idea is to reverse-engineer an understanding of soccer tactics from the tip of the pyramid downwards, from what you're ultimately trying to do (put the ball in the net) backwards to how you go about doing it. I'll pepper this with video examples where I can find them, but tracking down good examples turns out to be really tedious. One of soccer's great charms is the very many and very different approaches that are available, and which different teams have used to good effect. The game allows for such a diversity of styles which makes watching it all that much more engaging.

Here are the various ways people try to score from what is called 'the final ball in': how the striker receives the ball and deposits it into the net.
The first and simplest is to receive the ball, move past the defenders or into a gap and to shoot. Most goals you see in a casual kickabout or at junior level are like this, while almost none of them are at the top-level, on account of how much better defending is there. The ones that do tend to make the highlight reels, since it takes a lot of skill to just go through world-class defences. For instance, this one by Denis Bergkamp against Argentina in '98.
A less spectacular but no less lovely, and far more common, way goals are scored at the highest levels is when the striker is played into a bit of space by a short pass or a flick or header. Like here, Rivaldo scoring for Brazil against England in the 2002 WC: see how Ronaldinho draws the defenders to the left, and Rivaldo smartly makes just a few inches of extra space by stepping out to his right and clinically slotting it in. Great work off of the ball.
You can also play a striker in with a longer pass, like a through ball which runs between the defenders and which the striker runs on to. If a pass like this manages to connect, it's a great chance. The idea is that the attacker gets the advantages as he rushes past the defender, who loses time and momentum by having to turn around. Here is a great example, Ronaldo against Ghana in 2002.
Then there are final balls in which aren't aimed at anybody in particular, but which put the ball in an area where somebody might put it in. The idea is normally to move the ball across the face of the goal, where someone can run onto it, normally at one of the goal posts. You hear the phrase 'make a run to the near/far post' a lot, and strikers who have the off-the-ball nous and initiative to put themselves at the right place in the right time end up scoring a lot of goals. Here's a nice example of the Ivory Coast bouncing the ball to and fro in a very dangerous way, until the inevitable happens and Didier Drogba knocks it in against Argentina.
The long-ball equivalent of this is crossing: someone runs the ball along the flank and swings it to the near or far post.This is probably the most effective way to score at the highest level, since it's so hard to defend against them: the defenders have to stand and try to be where the ball gets within touch, whereas the attackers can run in and come at the ball with some speed and aggression. Crosses are either from the deep or the byline (the rear touchline), and crosses from the byline are much more dangerous as they square up the defence and very often teasingly swings out leaving the defence and falling for the attackers. Deep crosses are harder to convert because normally you are catching up on the ball from behind, making it harder to control. Nonetheless, it's one of those with which Winston Reid scored this one for New Zealand in stoppage time just a few days ago against Slovakia.

OK, so here are the ways teams try to set up the final ball in. There are basically three passing styles: direct, short and long.
Direct passing is just that: trying to get the ball straight to the striker in front of the goal. A direct passing game is often called 'route one football', very often consisting of long lobs into the opponent's penalty box. This is very common at lower levels of play, where a bit of good teamwork and sufficiently muscular play can lead to a lot of goals. This is also considered dreadfully boring to watch, and it doesn't require very much skill. Very often you have a tall and strong striker up front to act as a target man, getting onto the end of lobs and then either flicking the ball on for his strike partner, or doing something with it himself. Here's a rather classy example, from one of Beckham's famous crosses from the deep setting up an easy goal for Peter Crouch for England against Estonia in WC qualifying.
Long ball passing is often route one football, but is more varied and can be lovely. Ideally the ball lands behind the defence and the striker (or winger, or forward) runs onto it into space, either setting up a ball into the box or a chance to score. Through balls and crosses typically feature a lot. The first goal of this tournament, by Siphiwe Tshabalala against Mexico, is a fine example of long ball football.
Short ball passing is a favourite of teams with lots of individual skill, which it requires to pull off, because you need to string a lot of touches together without making a mistake. The example Chet linked to of Cambiasso capping a gorgeous Argentine move is a lovely one. The idea is to move the ball around a lot, seeing if you can draw the defenders out of their position and create a bit of space for something to happen.

OK, that's enough for now. I'll probably get back to this soon, but I don't want to burn either me or you out.

[Good Intentions]

Well, perhaps you're getting tired but here I am, back again.

Taking into account the resources available to the team, the look of the opposition and the type of final ball they're looking to put in, they can arrange themselves in various layouts. I'm not going to mention the formations now, but more the general shapes: teams can play wide or narrow, along the flanks or through the centre, and deep or compact. There's also having players behind or ahead of the ball.
A team playing wide tries to use the full width of the pitch in order to stretch out the opposition and create space for themselves. The usual tactic is to move the ball along the flanks, but some teams like to cut inside from out wide, first drawing the defenders out and then going inside of them. The problem with this is that space for you is space for your opponents as well.
A team playing narrow gets the players closer together in the centre of the pitch, allowing them to keep the ball close to them and perhaps outnumbering their opponents close to the action, but also giving up room on the flanks for the opponents to move into.
Playing along the flanks is often a good way to quickly get the ball up the pitch, possibly to swing in a cross. Sometimes a fullback will play to a midfielder on to a winger who puts the ball into the box, sometimes someone will punt the ball up ahead towards the corner flag for someone on the flank to run onto. Here's a good example of the former by the 1974 Dutch team, nicely moving the ball along and allowing Cruyff to do his thing.
Playing down the centre is more direct, but hardly excludes skilful play. It has the possibility of more players being getting involved, as those on the wings can step in to knock the ball back into the centre, often getting involved in one-two moves. Brazil historically likes to play this way, like this beauty by Éder in their gorgeous but ineffectual 1982 World Cup campaign.
Playing deep means that you're using more of the length of the pitch, typically allowing you to move the ball forward quicker since your players are already lining up towards the opponent's goal. The normal way to add depth to you shape is to play with the defenders further back towards their own goal, stretching out your players length-wise. The problem with this is that you're often leaving space just in front of your defenders that your opponent can move into and launch an attack from.
Playing with a compact shape, normally done by having the defenders further up along the pitch and having the forwards close to the midfielder, is often done in order to crowd the midfield. By having the defenders close-by there are more people to pass to-and-fro between and shorter distances to cover. Also, teams with speed up front can often try to speedy forward with a long ball behind the opposing defence to run onto, leading to good scoring opportunities.
You'll often hear about teams having lots of players behind/in front of the ball, typically referring to their shape when the opposition have the ball. As you might guess, this refers to how many players there are between the ball and your own goal. Having more players back closes the spaces your opponent might run into, and let's you have more people around to harry the attackers, pounce on loose balls, etc. The downside is that this is a rather negative way to play, since if you were to get the ball, there's almost no-one up front to receive it. It's very possible to play deep and with a lot of players behind the ball: counter-attacking teams do this often, with only a couple of players ahead of the ball but well up the pitch waiting for a long ball to latch onto and the opportunity to get behind the opposition and run at goal. The more players there are ahead of the ball, the more attacking resources and the more likely you are to pose a threat. This is probably the most important quality determining how attacking or defensive a team is: because football has so few stoppages, possession can change quickly and the ball can move so quickly up the field, play can move from one penalty box to the other in the blink of an eye, provided that there is someone there to receive it.

[Good Intentions]

OK, now on to the final push.

When talking about the shape of teams, we're already starting to talk about defence, since so much of what a team needs to take account of when arranging its own position is how to react to the opponent's moves. This leads us into the positional parts of defence: how far up the pitch the defence plays (including mention of the offside trap), normal defensive formations, defensive midfielders, and counterattacking from defence. There's also matters of how the defence responds to the opposition: whether they press or not, and the involvement of the midfield in defence. This isn't the type of thing that makes highlight reels, so it's something to keep an eye out for during the normal run of play. And that will be the end of my short primer to football tactics.

Normally defenders play in a lateral line, for a few reasons, an important one being the offside rule. If a defender is further forward than the line, he creates a gap for an attacker to run into. If the defender lags behind, his position can play an attacker onside which can lead to disastrous (for the defence) long balls or through balls latching onto a forward speeding away. The defensive line can be moved up and down the pitch almost as if it were controlled by a slider. The issue to take into account with how far up is where you want to close down space (and open it somewhere else). If your defence plays further up, they take away some of the depth the opposition might have hoped to use, but leave large gaps behind them where a forward might run onto a through ball or a long ball. If both sides play with the defence up, it forces a compact shape onto the match, which leads to some gritty midfield atritition with 20-odd players running into each other. Playing back, on to other hand, gives your opponent less space to run into behind you, but perhaps gives them space in front of you where they can roam in. These days, when a defence plays back to any real degree, they have 8 or 9 players behind the ball, so that the defending midfielders can close down any runs the attackers might make at the defence.
One way a defence can respond more actively to attacking threats is through the offside trap, where they play with an apparently staggered defensive line, but just before the attacking team tries to play a ball to a forward, the backward defenders rush forward to join the defensive line, leaving the attackers in an offside position. This can very effectively shut down attacks. But, it only needs to go wrong for the defence to end up with egg on their face, since the way you're running to effect the offside trap is the opposite way from where you should be going to defend against an attacking run. You don't see all that many teams playing the offside trap these days, not at World Cup level at least.
These days almost all teams play with four men back: two centre backs and two fullbacks, one on each wing. This allows the centre backs to handle any runs by the strikers and long balls into the box, with the fullbacks covering any runs that wingers might make. Since most attacking teams have two strikers and two wingers making runs, this works out very well for defence. When their team has the ball, the fullbacks often move forward to support the attack, getting more and more involved in recent years. Those two factors together probably lead to the ubiquity of having four at the back.
Sometimes teams play with three central defenders at the back. These days only really defence-minded teams play this way, though it needn't be so. Sweepers used to be prominent, but I haven't seen one in years, except for when a player temporarily plays that role when his team has a lot of players behind the ball. A sweeper lurks around in front of the keeper, latching onto any dangerous balls or runs that might pop up.
It's not just the four defenders that actively defend the goals during open play. Since the space in front of the defensive line is so important, teams do well to have a defensive midfielder patrolling it. They almost act like sweepers do, except in front of the defensive line instead of in front of the byline. Very often they also play a holding role, meaning that they'll stay on the ball as the other players rush forward, and then play the ball forward once the attackers have gotten into promising positions. In the Peter Crouch goal I linked to in the OP, Gerrard has done just that: he's picked up the ball somehow (won it in a tackle or made an interception), looked up, saw Beckham in some space, and moved the ball along from where Becks did what Becks does and makes someone else look good. These days the two roles, defending and  holding, get split more and more, with holding midfielders often being more like playmakers rather than defensive terriers. This doesn't change the fact that DMs typically run the most of anybody on the team (unlike sweepers, who can get away with being a little slower off the blocks).
A good rule of thumb for a team looking to have balance is to have five defence-minded players and five attack-minded players in the outfield. Normally this is the back four supported by a defensive midfielder, holding the fort while the wingers, strikers and an attacking midfielder look to go forward. It's more a matter of mindset than of position: in most teams, the defensive and attacking midfielders are alongside each other, but the DM looks to fall back and snuff out trouble, and the AM is itching to run forward and run onto whatever ball the DM might have poached and is looking to move forward.
An increasing feature of the modern game, though, is that fullbacks are becoming more and more aggressive. You now quite commonly get something called 'overlapping fullbacks', where the fullback barrels forward along the sideline, running onto a ball that the winger or a midfielder flicks on for them, and then the winger falls back to cover the gap the fullback has left. With the players moving around and changing position, a defence has to work hard not to lose track of exactly who is posing a threat and who not, and overlapping fullbacks also add some variety to the attack. The problem with this maneauver, and having fullbacks come forward at all, is the gap they leave: the corner-flag area is always an excellent place to lob the ball to on the counter-attack for a forward to run into, and doubly so when the fullback doesn't only have to turn around but also has to run back for 50-odd yards. Midfielders are supposed to cover overlapping fullbacks, but they're midfielders and not defenders and many attackers will take their chances to try and get past them.

When a team is off of the ball, they can either try to press the opposition or not. Pressing involves running at the attackers, getting in their face, putting them under pressure and trying to force a mistake, either tackling the ball off of them or forcing a bad pass that you can intercept. Stealing possession in this way can very easily lead to a good attack: as a team attacks, they commit players from the back forward, leaving spaces. If a defender (especially a DM) snaffles the ball they can quickly shoot the ball forward to a winger or a target man, and suddenly someone is in on goal. The problem with pressing is that if the attackers are sufficiently skilful they can make the defenders look very silly: jinking past the onrushing defender, for instance, tiring them out with lots of short passes, and so on. This gorgeous example at the highest level of club play, Barcelona vs. Liverpool, has Barca playing a short passing game through the centre with a wide, deep shape, ending with a lovely through ball once they got the Liverpool back line out of shape.
Correspondingly, when a team plays with many men behind the ball, they tend not to press that much, inviting the attackers to try and squeeze between them. This can be very hard to break down. I haven't mentioned long shots, because they only work in highlight reels and video games, but this is where they come handy. If a player is under no pressure they can set up a scorcher of a shot, like Reyes did here in his Arsenal debut against Chelsea. And even if it doesn't go in, if they force a save off of the keeper, someone might be able to pounce on the rebound, or force a corner. Still, it's not a high-percentage play.

Well, that's it. There's far more to say here, especially about the typical roles of the various types of players on the field. I've talked a bit about the movement of wingers and fullbacks and defensive midfielders, but that's because their roles are so intimately linked with how the team as a whole is moving, and these big-picture tasks by no means exhaust what those players do on the field. I haven't mentioned set-pieces at all, but they're pretty easy to understand (though there's some tactics involved here as well). But this is the short introduction, after all.

[lucky strike]

this thread is great and has been very informative to me so far. i hope there is more. also:
This gorgeous example was so incredible i nearly wept

[kyle]

Hehe, I really enjoyed the read, hopefully others did as well back then.

Have you ever checked out zonalmarking.net? It's a soccer tactics website. Interesting to read.

[Good Intentions]

I go there at least twice a week.

[Good Intentions]

Another good site is www.footytube.com , which is an aggregator for football videos on Youtube, etc. Most of those are just minute-long highlight reels, but you can often enough find 5 or 10 minute (or even longer) compilations which show you a lot of the lead-up to the highlights. It's far more interesting that way.

[Good Intentions]

Triple post of power!

Sometimes you get a beautiful synergy between those two sites, like when a zonalmarking.net analysis and a lengthy highlight reel exist for the same match. And it helps that it's one of the bigger derbies in the world.