One of the key ideas to understanding how Mauricio Pochettino's Tottenham press the ball is understanding the cues that trigger the press. Even if Pochettino is aggressive by Premier League standards, compared to Jurgen Klopp or Roger Schmidt he is actually fairly conservative.

His Spurs team is not the sort of "heavy metal" all action pressing machine that they are sometimes made out to be. Rather, like all teams they press in specific situations and, in their case, their aggression as to when they press falls somewhere between a low-block, highly selective pressing team like Diego Simeone's Atletico Madrid and the far more aggressive approach of Roger Schmidt's Bayer Leverkusen.

If a ball is played backwards straight into the feet of a center half facing downfield, you won't see Pochettino teams pressing the ball for the simple reason that they are virtually certain to not win the ball and, by pressing and failing, they will lose their defensive position and create dangerous passing opportunities for the opposition.

In contrast, if a ball is played into a defender facing his own goal and he has to turn on the ball before playing a pass (or pass it back to his keeper) you will likely see a press. This is, for example, how Spurs scored their opener at the Emirates in last year's first North London Derby.

One of the most common areas where the press is triggered is on either flank. If you watch basketball, you understand why: If a player receives the ball in the center of the park, he can turn 360 degrees and play the ball in any direction. But on the wings he has only 180 degrees that he can use to play the ball because the sideline cuts him off.

Thus it is much easier to trap him and win the ball. You can see this approach if you look at the defensive actions that Spurs advanced midfielder attackers make in a typical game. Below is Erik Lamela's defensive actions map from the 4-1 win against Manchester City:

Note that six of the seven attempted tackles happen close to the sideline. Note also that he has a 66% success rate on the three challenges closest to the sideline and only a 50% success rate on the four further from the sideline. Pressing aggressively on the flanks is one of the best ways to win the ball and spark a quick attack.

However, pressing effectively on the edge requires more than just one or two players to be effective. The whole team shifts left or right in order to squeeze the entire space. The idea is to not only close down on the man in possession, but to also cut off all the available passing lanes to players near him. If you fail in that, then when he does evade the immediate pressure closing on him the man in possession can pick out a teammate who will be in a relatively large amount of space.

This is something Lucien Favre's Borussia Monchengladbach did quite masterfully last season. They squeezed the opposition on either sideline by shifting as an entire team left or right as needed. On its day it could be devastating.

Fast, technically adept teams can beat this defensive system.

The obvious weakness with this approach is that if the opponent does switch play, you're likely going to concede a good scoring chance.

You can see this problem in the buildup to Swansea's first goal as Jefferson Montero gets ready to receive the ball on Swansea's left wing. In the above image Kyle Walker and Erik Lamela are the players closest to Swansea's left wing and yet both of them are actually in basically the center of the field:

In most cases, however, this isn't usually a major concern because the immediate pressure on the man in possession from the closest two players makes it difficult to play long cross-field passes. Then if the other eight outfield players also shift to cut off the midfield passing lanes it also becomes difficult for them to move the ball cross field through two or three quick passing moves. So this is an obvious weakness, but it's not actually an easy weakness to exploit.

However, if you face a team with intelligent, fast wingers and energetic passing midfielders you can run into trouble because that is the sort of team that can usually beat the press in wide areas.

Swansea City, unfortunately for Spurs, is just such a team. With three industrious passing midfielders staying in the center of the park and two quick wingers the Swans are perfectly equipped to attack Tottenham's aggressive scheme.

How did the goal happen?

On the first goal, the problems began when Tottenham tried to press in a situation where they probably couldn't win the ball. Federico Fernandez receives the ball facing downfield with multiple easy passing options. It's not a great opportunity to win the ball, but Eriksen attempts to anyway:

Eriksen and Chadli chase the Swans defense around a bit, but they never get close enough to actually make a tackle or win possession. (Note that Fernandez also made a clever run to make himself available to Angel Rangel. This is one of the most important parts of the goal because it gives Rangel the chance to play the ball forward when Eriksen presses him. If Fernandez stays deep, then Rangel will be forced to play the ball backwards and the press won't be broken.)

When Eriksen and Chadli initiate the press the whole team shifts toward that side of the field to try and squeeze the play. So you see Lamela, Alli, and Dier all moving toward the right in the GIF above. Tactically speaking, this is a good thing. This is how the system is meant to work.

Unfortunately, Ayew is able to get loose and receive the ball and play it forward to Gomis. Gomis lays it off for Sigurdsson who now has an easy pass out to Montero at which point Spurs are in trouble:

From here, Montero chips his cross into the box and Ayew heads it home to give Swansea a 1-0 lead.

Is this more of the same failed pressing that we saw last season?

Actually, it isn't. Last season the problem in most matches was that the team didn't move as a unit. Brett has analyzed that problem here. This year we generally haven't seen those kind of defensive breakdowns. (Brett has you covered on this point too.)

In the above situation the problem is not that one guy missed his defensive cue and broke the system. In this sequence, the entire team is moving as a unit. Chadli and Eriksen initiate the press up top and the entire team responds. That's not the issue. Nor, for that matter, is the issue necessarily with Walker's handling of Montero in that one-on-one situation. To face a player like Montero in that much space and hold him to no more than a cross (generally a low-percentage attacking move) is actually pretty good. A lesser player may have let him get inside for a shot or fouled him in the box to concede a penalty and likely pick up a yellow card, which would force the team to radically change its defensive approach in order to protect him from picking up a second yellow. (Gareth Bale routinely did this to fullbacks during his days as an orthodox wide man.) Walker used his pace to keep up with Montero and was smart enough to keep him wide. That's all good.

Really, the issue here is that Spurs' system basically did what it is supposed to do; they just never won the ball. And that is probably more attributable to Swansea's quality than to Tottenham's failings.

Conclusion

In a weird way, this opening goal from Swansea should actually be an encouragement to Tottenham fans. To review, here's what happened on the goal:

Eriksen and Chadli tried to win the ball in a dangerous area in the attacking third with Kane lurking on the edge of the box. This is a good thing.

The entire team reacted to Eriksen and Chadli initiating the press by shifting laterally to squeeze the field. This is a good thing.

Kyle Walker did not allow Jefferson Montero to get inside nor did he attempt to make an ill-advised tackle in the box that resulted in a penalty. Instead, he managed to limit one of the Premier League's in-form wingers to a mere cross after being put in a dangerous one-on-one situation. This is a good thing.

Sometimes an opponent scores a goal because they simply earned that goal. That's what happened here with Swansea. The quick ball movement under pressure, the intelligent movement from Federico Fernandez to make himself available to Angel Rangel at the start of the sequence, the clever one-touch passing from Gomis and Sigurdsson, the nice cross from Montero, the wonderful header from Ayew... this was a quality goal from beginning to end. And while you could snatch at things a bit and try to pin the blame on a Spurs player – Eriksen for initiating the press, Dier for perhaps pressing too far up the field and leaving Sigurdsson in space, Walker for allowing the cross, Vertonghen or Alderweireld for not getting tighter to Ayew – the fairest thing to do is simply salute a marvelous team goal from Swansea.

As far as Tottenham go, the system was working – that's why Swansea wasn't able to successfully break the press for a second time. It just got beat by a very good team.

Spurs fans, because we're Spurs fans, will want to focus on that second sentence. But in this case we'd probably do well to focus primarily on the first one.