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Friday, June 21, 2024 | Back issues
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Virtual Reality Reveals Fatal Flaw in Soccer’s Free Kick

A goalkeeper’s ability to stop free kicks can make or break any football team. But virtual reality shows the defensive wall of players meant to block the kick may be more of a hindrance than an aid.

(CN) — A goalkeeper’s ability to stop free kicks can make or break any football team. But virtual reality shows the defensive wall of players meant to block the kick may be more of a hindrance than an aid.

The revered game of football, or “soccer” as it’s called in the United States, is set by fielding 11 players from a team against 11 players from an opposing team. Included in the batch of athletes are two goalkeepers on opposite ends of the field who are tasked with stopping the ball from crossing the goal line in their respective posts. 

During a game, free kicks represent a unique goal-scoring opportunity typically triggered when a player commits a foul on an opposing player near the defending goal. Rules require the ball be at rest while the defending goalkeeper lines up his teammates in a wall of bodies meant to make it more difficult for the attacking team to score.

Once the play is set and the referee blows their whistle to initiate the kick, a mix of talent, fate and luck dictate whether the ball bulges the goalie’s net or not.

Researcher Cathy Craig of Ulster University in Belfast said in a statement released with the study that understanding the goalie’s thought process is critical to understanding the play.

“Although goalkeepers might claim to ‘see’ the ball through the wall of players before it is kicked, they will most likely not see how that initial part of the ball trajectory unfolds just after it has been kicked,” Craig said. “It’s that important information the brain needs to make a decision about where the ball is going and when it will get there.”

To understand free kick outcomes more comprehensively, a team of Northern Ireland-based researchers dug deeper into the ritual and examined what role, if any, the defensive wall plays in shaping the score line.

Removing the need for a wall of real players, researchers used virtual reality to simulate a free kick and study the goalkeeper’s reaction to it based on both flight trajectory and the wall’s position.

Using both novice and skilled goalkeepers, researchers measured how the defensive wall’s placement impacts a goalie’s initial movements once the ball leaves the attacker’s foot. 

In elite football leagues, the ball can reach a goalkeeper in less than a second from within 33 yards of the goal.

The study found having a defensive wall may result in conceding more goals because it impedes a goalkeeper’s view of the kicker and delays quick tracking of the ball’s trajectory, according to the study published Dec. 23 in the journal PLOS ONE.

“The effect was substantial and consistent enough to warrant the suggestion that goalkeepers should evaluate whether placing a wall is always their best option,” researchers wrote in the 20-page study. “For instance, when faced with a free kick expert whose shots on goal are hardly ever blocked by the wall, the only possible goalkeeping benefit of the wall would be preventing some more challenging shots.

“Scientifically, the relative contributions of various effects of the wall on the goalkeeper (e.g., occlusion of the kicker and initial ball trajectory) and kicker (i.e., aiming benefits and kicking strategies) remain to be determined–such knowledge evidently is also highly relevant for practical impact.”

For both novice and skilled goalies, the presence of a defensive wall significantly impacted their ability to stop the free kick, especially if the kick was taken from a central position facing the goal.

The results should not be taken as evidence that defensive walls should be abolished, researchers said in the statement, adding that teams can instead evaluate the findings to determine whether a defensive wall is a good tool or not.

“We are not suggesting goalkeepers should never use a wall, but we are saying they should consider whether the benefits of placing a wall outweigh the negative effects of not seeing that initial part of the ball flight,” Queen’s University researcher Joost C. Dessing said in the statement.

But the study also affirmed that expert free kick takers have been exploiting the “occlusion” for decades, knowing the wall can be an asset for the attacking team.

“Clearly, wall-induced occlusion renders the free-kick scenario a game of cat and mouse between the attacking and defending teams,” the study said.

Co-authors of the study include Theofilos Valkanidis and Alan Cummins of Queen’s University Belfast

Based on the research, Craig has developed CleanSheet, a virtual reality tool to help goalies prepare for free kicks.

The study was funded by the European Union Seventh Framework Programme, the European Union's Horizon 2020 and the European Research Council.

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