The Space Behind the Fullbacks: Vietnamese Football's Biggest Tactical Puzzle in the Kim Sang-sik Era

The twelfth minute of a match whose every run I still remember clearly. The team in red built up from the right wing, with the fullback pushing high almost to the halfway line to apply pressure. The ball switched to the opposite flank in two passes. And when I rewound that footage for the eleventh time, I paused on the frame just as the goalkeeper prepared to take his goal kick: behind the left fullback, a patch of ground nearly twenty square meters wide was completely empty. No one was there. Over the next forty seconds, that patch was exploited, and the goal conceded came from exactly the spot the naked eye ignores. From that first mistake, I learned to read a match through space.

That was not a mystical moment. It was geometry. In modern football, when the fullback is one of the positions asked to run the most, and simultaneously the position most often left vacant when the team loses the ball, the question is no longer who is better than whom. The question is who controls the space before the opponent even thinks of it. I have spent most of my commentary career dissecting exactly one thing: not the ball, not the men, but the void both leave behind them.

Vietnamese football, at this moment, stands before a structural problem directly tied to this space. This is what I want to dissect in today's long analysis, as someone who has followed Asian football in general and Southeast Asian football in particular for many years, and as someone who sat in Kazan in 2026 and witnessed a historic, decisive space.

Let me be clear from the outset: this is not an article about a single win or a single defeat. It is about how a football nation builds and breaks spatial structures, and why Vietnam stands at a tactical crossroads.

Context: A football nation in structural transition

To understand why the space behind the fullback has become the focal point, we must place Vietnamese football in its proper context. Over roughly the past decade, Vietnamese football has shifted from a game based mainly on quick counter-attacks, long balls and physical strength toward one that seeks to control possession more, build from the back and circulate the ball through the lines.

This shift did not happen overnight. It began with generations of players trained methodically at academies such as Hoang Anh Gia Lai – JMG, PVF, and the youth setups of the big clubs. These players grew up with a different footballing mindset from the previous generation: they were taught to receive the ball under pressure, to turn, to find space between the lines.

At national-team level, this process is tied to different coaching regimes, each bringing its own philosophy. There was a period when Vietnam played with a back three, exploiting two extremely energetic wing-backs. There was also a period when the team reverted to a back four with a diamond midfield. Every formation change redrew the entire spatial system.

Currently, under coach Kim Sang-sik, the Vietnamese national team is undergoing a period of restructuring. Kim Sang-sik is a Korean coach who brings Korean football thinking: spatial discipline, organized pressing, and rapid transitions. A Korean coach leading a Southeast Asian national team creates a fascinating crossover, and also some tactical tensions I will analyze later.

The V-League, the club-level competition, reflects this shift too, but at a different pace. In the V-League, the quality gap between big and small clubs remains quite clear. Strong clubs such as Cong An Ha Noi, Thep Xanh Nam Dinh, Hanoi FC and Hoang Anh Gia Lai tend to control possession and push their lines high. Weaker clubs usually choose a low block and counter-attack. This very stratification creates the perfect environment for the space behind the fullback to become a decisive weapon.

I want to anchor the entire analysis with one concrete fact. According to data I collected and cross-checked from various match-tracking sources in the V-League in recent seasons, goals from attacks exploiting space in the wide channels account for a substantial share of all goals, especially in the second half, when fullbacks' physical capacity declines. This is no coincidence. It reflects a rule: when the line pushes high, the space behind is the price to be paid, and whoever pays that price later wins.

Tactical analysis: Dissecting the space

Here I need to redraw the spatial map so readers can see what I see. Imagine a pitch with a 4-2-3-1, now the popular formation at many Vietnamese clubs. A back four. Two central midfielders. Three attacking midfielders. One centre-forward.

When the team has the ball and attacks, the two fullbacks push up almost simultaneously with the two wide attackers. This creates a numerical advantage in both channels. But it simultaneously creates two lethal gaps: one behind each fullback, and one in the middle if the two central midfielders are dragged wide to cover.

This is the point I want to emphasize: space is not where the ball is absent, but where the ball will arrive if you do not prepare in advance. A fullback pushing high is not wrong. The error lies in the team having no mechanism to cover that space.

Mechanically, there are three ways to cover the space behind a fullback. The first is for a central midfielder to drop deep, forming a three-man line at the back, turning the back four into a back three in possession. The second is for the opposite fullback to tuck inside, forming a three-man spine in the middle. The third is for a centre-back or defensive midfielder to act as a screen, sweeping the space when the team loses the ball.

Interestingly, in Vietnamese football, all three mechanisms sometimes exist but not in sync. Some teams drop a central midfielder but let the opposite fullback push up unchecked. Some tuck the fullback inside but have no one to sweep the middle. Some have a screen, but the screen runs toward the ball instead of into the space where the ball will arrive.

I have spent many evenings analyzing V-League and national-team matches, and each time I am reminded of that afternoon in Kazan in 2026. That day I sat in the stands with a small tactics board. Before kick-off I pointed at the diagram and told the colleague beside me: the opponent's fullbacks will push high, and the space behind them is where the goal will come from. I am no prophet. I merely read geometry. And when the goal came exactly as predicted, I understood that football, at its deepest layer, is a sport of space.

Apply that logic to Vietnam. When the national team faces opponents physically and athletically stronger, such as Japan, South Korea or Iran at continental level, pushing both fullbacks high is a gamble. If the midfield lacks the ability to hold the ball and slow the opponent's counter-attack, pushing high exposes space to an opponent capable of transitioning in just two passes.

Conversely, when Vietnam faces weaker Southeast Asian opponents, pushing high is necessary to apply sustained pressure and break a defensive block. But even then, the space still exists. It is just that opponents are less able to exploit it precisely.

This leads me to a structural judgment: Vietnam has a squad built to control possession in Southeast Asia, but not yet a structure safe enough to take risks at continental level. The gap between these two objectives is the gap in the mechanism for covering space.

Let me speak more concretely about data. In modern analysis, I regularly use two indicators. One is PPDA (passes allowed per defensive action), which measures pressing intensity. The other is field tilt, which measures a team's dominance of attacking space, usually calculated as the ratio of touches in the opponent's final third to total touches in both final thirds.

When I compare these indicators across V-League teams, a pattern emerges. Teams with high field tilt, meaning good control of attacking space, tend to have low PPDA, meaning high pressing. But the paradox is this: these same teams are also usually the ones most exploited behind the fullbacks, precisely because they push their lines high and leave space.

This is the essence of the trade-off in modern football. You cannot simultaneously press high, control attacking space, and leave no space behind. You can only choose to manage that space better than your opponent.

I want to use this section to discuss an aspect few notice: the centre-back's role in controlling the space behind the fullback. When the fullback pushes high, the centre-back on that side must decide two things: track the opposing centre-forward, or pull wide to cover the space. This is a decision of only a few tenths of a second, and it depends on whether the centre-back can read the opponent's intention.

In the V-League, I observe that many centre-backs tend to mark the man rather than the space. This is reasonable in traditional football, where centre-backs are taught that their job is not to let the opposing striker escape. But in modern football, when teams attack by dragging centre-backs out of position to create space for others, marking the man can become a weakness.

I recall watching a V-League match in which the defending team had two very solid centre-backs. But in the second half, the attacking team repeatedly dragged one of them wide through the centre-forward's movement. And each time, space appeared in the middle. The goal did not come from the wing, but from the middle, after the centre-back was dragged out. That is a textbook example of a wide space opening a central space.

This confirms a principle I believe in: football is an interconnected spatial system, where a space opened in one place creates a new space in another. You cannot compensate for one space without opening another. The art of tactics lies in choosing which space to open, and which to protect.

At national-team level, Kim Sang-sik is trying to apply a more balanced structure. From what I observe in Vietnam's matches, the team usually uses a deep-lying central midfielder to form a three-man line in possession, while the two fullbacks alternate in pushing high. This system helps control the middle better, but also demands that the central midfielders read space very well.

The problem is that when a central midfielder drops deep, he can no longer support defending in the two channels. And if the opposite fullback also pushes high, the space in the channel becomes wider. Vietnam sometimes struggles against opponents' rapid transitions, where the ball is switched from one flank to the other in a single long pass.

Here I return to the Kazan memory. In that match, my team prepared thoroughly for the ability to exploit the space behind the opponent's two fullbacks. The principle was simple: when the opponent pushes high, let them push high, and attack the space they leave. Football is not about stopping your opponent from doing what they do well. Football is about turning what they do well into their weakness.

Applied to Vietnam, I argue that Vietnamese teams need to train their ability to attack the space behind opponents more systematically. Currently, many V-League counter-attacks rely on the speed of one or two individuals rather than a well-drilled transition structure. This makes counter-attacks unstable and easy to neutralize against well-organized opponents.

A good transition system needs three elements. First, a player able to deliver the decisive pass in tight space. Second, a runner able to read the timing and direction of movement. Third, a team structure that allows the first two to connect in the shortest time.

In Vietnamese football, I see the first and third elements improving, but the second still lacking stability. There are very intelligent runners, but not enough of them to form a trend. And when quantity is insufficient, the quality of transitions depends on luck.

I want to add a note on the role of wide attackers in controlling space. In many modern formations, wide attackers tend to invert, or move into the spaces between the opposing fullback and centre-back. This creates a different attacking model: instead of attacking by pushing fullbacks high, the team attacks by letting wide midfielders move inside and the fullback hug the touchline.

This model, which I call the "inverted wing" model, has the advantage of keeping the defensive structure more stable, because the fullback does not need to push excessively high. But it also has a drawback: it does not create overlap in the channel, and it demands that the wide midfielder handle the ball very well in tight space.

I have a personal view on this trend, and I will say it plainly: the homogenization of wingers into inverted players is stripping away part of football's identity. I believe the traditional winger, capable of hugging the touchline, dribbling past opponents and crossing, is being unfairly undervalued. In Vietnamese football, where individual technique and dribbling are among the traditional strengths, abandoning the traditional wing model entirely could be a strategic mistake.

Look at the reality of Southeast Asian football. Teams in the region usually lack superior height, but have speed and technique. In that context, using traditional wingers, who can make the difference in one-on-one situations, may be more effective than trying to imitate European models that demand physicality and height.

I do not deny the value of modern models. I only question applying them mechanically without regard to the characteristics of the human resources available. The best tactic is not the most advanced tactic, but the tactic best suited to the people you have. This is a principle I learned over many years working with coaches and players.

Contrarian view: The blind spot in execution

Here I want to offer a view that may be controversial, but I believe it needs to be said.

In many discussions of Vietnamese football, people tend to focus on the lack of good players, the lack of international experience, or the lack of investment. I believe these are real problems, but they are not the biggest blind spot. The biggest blind spot is this: Vietnamese football is trying to solve the space problem by buying more players, rather than by changing the structure.

I have witnessed this throughout my career, in many football nations. When a team repeatedly concedes because of space behind the fullback, the coaching staff's first reaction is usually to find a faster, stronger, better fullback. But if the structure does not change, even the best fullback will be exploited, because space is a consequence of structure, not of individual quality.

This is a paradox I want to emphasize. In football, upgrading individuals can mask a structural problem in the short term, but cannot solve it in the long term. A good player can run faster to cover space, but he cannot run faster than the ball. And in modern football, the ball always moves faster than the man.

I want to tell a story from my experience. There was a period when I worked with a youth team, and the head coach repeatedly asked me to analyze why the team conceded so many goals from the flanks. I reviewed dozens of matches and reached a conclusion he did not want to hear: the problem was not the fullback, but the team's lack of a mechanism to cover when the fullback pushed high. He changed three different fullbacks in three consecutive matches. The result did not change.

The lesson here is: when a problem recurs with different individuals, the problem lies in the system, not in the individual. Vietnamese football, at this moment, has an opportunity to reconsider this problem seriously.

The second blind spot I want to mention is how we evaluate young players. In many places, including Vietnam, young players are usually judged mainly on individual technique and speed, while the ability to read space and make decisions is given less weight. This is a mistaken trade-off, because individual technique can be improved over time, but the ability to read space is a skill that must be trained very early.

I believe that if Vietnamese football wants to go further at continental level, it must change how it develops youth. It must teach young players not only how to handle the ball, but how to read the match as a spatial map. It must teach them that their position is not a fixed point on the pitch, but a dynamic relationship with the ball, teammates and opponents.

Here I return to my own story. I was born into a family with no sporting tradition. I came to football through observation, not through playing professionally. And perhaps that is precisely why I see the match differently. I do not see players as heroes, but as points in a spatial network. I do not see goals as moments of transcendence, but as the result of a chain of spatial decisions.

This view may be considered cold. But I believe football needs both ways of seeing: the emotional view of the fan, and the analytical view of the professional. Both are right, and both are necessary. What matters is not letting one view deny the other.

In the current transfer window, I observe a familiar phenomenon: clubs pour money into famous attacking players, while defensive positions and players able to read space are usually undervalued in the transfer market. This is a systemic imbalance, and it directly affects the tactical quality of teams.

A team can have the strongest attack in the league, but if its defensive structure is not solid enough to protect space, it will not win the title. Football history is full of examples of brilliant attacking teams that won no trophies because they conceded from small spaces. And conversely, modest teams with scientifically structured defenses often go further than expected.

I want to offer a conditional prediction to close this section. If Vietnamese clubs continue to prioritize buying attackers without improving their spatial defensive structure, then within two to three years, we will keep seeing matches where the better-playing team loses because of a momentary lapse in the wide channel. Conversely, if at least a few clubs pioneer in building a methodical spatial defensive structure, they will become models for the rest of the league.

I have a deep belief about Vietnamese football. I believe its potential does not lie in producing a superstar attacker, but in building an intelligent tactical system suited to its human resources. This is the harder path, but the more sustainable one.

Takeaway for the next match: What to watch

As I write these lines, I am not trying to offer a final conclusion. Football has no final conclusion. Football only has questions answered temporarily, and new questions raised.

In the upcoming matches of the Vietnamese national team and V-League clubs, I will watch three things. First, how the mechanism for covering the space behind the fullback will be implemented. Second, how teams transition from defense to attack, and whether they exploit the space opponents leave. Third, whether coaches dare to be patient with a new structure, even when short-term results do not come immediately.

These three things cannot be measured by goals. They can only be measured by rewatching footage, counting how often space is exploited, and cross-checking against the match result. This is how I have worked for many years, and this is how I advise football analysts to work.

Look at the space, not the ball. Look at where the ball will arrive, not where it is. And remember that in football, as in life, what decides the game is usually what the naked eye cannot see.

From that first mistake, I learned to read a match through space. And I am still learning, every match, every empty patch of ground, every decision that lasts only a few tenths of a second.