9 May, 2018

Spaces in Soccer from a Quantitative Perspective

Team Sports
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In the words of Johan Cruyff, “Players, in reality, have the ball for 3 minutes, on average. So, the most important thing is: what do you do during those 87 minutes when you do not have the ball? That is what determines whether you’re a good player or not.”

The development of the game through ball possession is the premise of the most studied and analyzed teams in recent years. Beyond the basic idea of simply “controlling the ball for as much time as you can,” these game situations include a long and important sum of actions with and without possession of the ball to create better opportunities for scoring. For example: creating different kinds of superiority, creating disorder in the defense through certain movements, building the game starting from the goalkeeper, etc. With all of these actions, there are two underlying concepts: creating and occupying space. These two concepts have always been a recurring topic for tactical analysis. However, this analysis has always been carried out through subjective observation by coaches and analysts, without being deeply explored from a quantitative perspective. Javier Fernández (Lead Data Scientist and Researcher for FC Barcelona) and Luke Bornn (of Simon Fraser University, Sacramento Kings) presented an article at the ’12th Annual MIT Sloan Sports Analytics’ Conference, which took place on February 23-24, 2018 in Boston. They propose a model for quantifying the occupation and creation of valuable space during open play. In the article, occupying space on the playing field is defined as the continuous position of a player in a specific area. At the same time, the value of this occupied space is quantified by the position relative to the ball, the proximity of the target to the opponent, and, more specifically, the level of possession of the space in relation to the number of opponents in a given area. On the other hand, “space creation” is defined as the action of moving opponents away from certain areas to create spatial availability in areas of the field that were previously covered. With these two measures, the authors propose a revision of the concept of controlling the field of play. In literature until now, this concept has always been discussed in terms of the division of space in Voronoi Tessellations, which considers the position of all the players on the field and calculates the player closest to each given point in space, finding dominant cells for each player. However, this focus does not take into account that the distance between the players and the ball is also influenced by the relative position and degree of control of the space – especially in sports with a large field, like soccer. The field control model presented by Fernández and Bornn is based on defining each player’s different levels of influence in the space based on their position and speed in relation to the ball. When a player is close to the ball but the ball is moving away from their position, the player is less likely to reach it. In contrast, if the player is far from the ball, but the ball is moving in their direction, their level of influence will be higher. In turn, the speed of the player has an important role in defining the area of influence. A player who is able to reach high speeds has greater influence on an area in comparison to players who are walking or jogging. To define the control of the field of each team, the authors consider the influence of each player in each point in space and assign a control value as a result of all these individual influences. Control of space is a fundamental element for identifying occupation and creation of space; however, we are still missing another part of the equation: The value of the space. It can easily be argued that not all spaces on the field have the same value. A simple method for determining the value of a space would be the distance from the opposing goal. A priori, spaces that are close to the goal have greater value, given the advantage they would provide if they were controlled. But because of the unique dynamic of soccer, the value of a space changes constantly depending on multiple factors, such as the position of the ball and the players.

Space Occupation Advantage

Given the dynamic nature of soccer, players are involved in a continuous process of gaining and losing space. A small gain in space can be made when nearby defenders follow the ball as it moves away from the player, leaving the player with greater control of the space. However, the same can occur between an attacker and a defender in a high speed running situation, where the attacker moves slightly faster. In another case, an average or large space gain can occur when a player moves toward a free space. For this reason, the level of space gain needs to be defined from whether the space gained can be considered an actual occupational advantage, rather than a consequence of slower-moving contextual factors in a given situation.

Space Creation Advantage

The creation of space for players is a concept that involves two or more teammates during a certain attacking situation. Two main types of actors are present: one creator and one or more receivers. The creator is a player who moves toward a certain space while dragging opponents in the process. This dragging behavior frees up space that was previously occupied by the opponent who was dragged. When that opponent was previously close to one or more teammates, we say that those players are receiving space created by the player who attracted them. A first step in quantifying the game without a ball Creating and occupying spaces are two commonly practiced concepts in modern soccer. During the training process, the coaches interrupt and restructure exercises to teach the players to orient themselves to move toward certain spaces and far from areas of low value on the field. The model proposed by Fernández and Bornn can be a first step in quantifying these concepts, including the contributions of each player in their movements without the ball. To access the publication “Wide Open Spaces: A statistical technique for measuring space creation in professional soccer, click here.

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