Offside in the Bundesliga: Pretending false facts
As of: April 29, 2026 9:27 a.m
When it came to offside, it used to be said: in case of doubt, for the striker. Today, semi-automatic offside detection is intended to provide clarity. But technically the VAR is actually blind for a certain period of time. How accurate and fair is it really in the famous “Kölner Keller”?
The second half has just started, that’s it Werder Bremen at 1. FC Cologne already back 0-2. 29th matchday – relegation battle. In the 47th minute, Cologne’s Alessio Castro-Montes was sent on and the Belgian pushed the ball past Werder keeper Mio Backhaus into the goal. Big cheers from FC and its supporters. But the celebration doesn’t last long. The VAR from the “Kölner Keller” switches on and indicates an offside position.
The animation shown on TV confirmed the decision shortly afterwards: When Ragnar Ache passes, Castro-Montes’ knee should protrude a little further than the Werder defender’s shoulder. “A millimeter, a millimeter – honestly, the technology should really be very precise,” says the sports show commentator. But is she really?
Scientist Weber: “They have a huge measurement inaccuracy”
Dr. Tobias Weber can only shake his head about it. The space scientist has been working at the European Space Agency (ESA) for over a decade and in his job he is intensively involved with a similar camera system that the DFL uses in football stadiums for its offside technology.
Space scientist Dr. Tobias Weber criticizes the offside technology in the Bundesliga.
He comes to the conclusion: “The fan is being led to believe something. They have a huge measurement inaccuracy and still make decisions that are in the range of millimeters or centimeters. That makes no sense to me.”
Space travel and football use similar technology
Weber is the lead scientist for a new training device that will soon fly to the international space station ISS. In order to observe the astronauts during their training in space on Earth, ESA uses a so-called motion capture system. A similar camera technology to the VAR in football. Same sampling rate, same pixel rate.
VAR blind for a certain period of time
Weber is also a football fan and likes to get involved – but recording the players in possible offside decisions causes him a lack of understanding. “The biggest problem is the sampling rate,” he says. “They use cameras that record at 50 Hertz, i.e. at 50 frames per second. The problem is: If you record at 50 frames per second, then you have a time between the frames in which you basically see nothing.” The VAR is therefore blind for a certain period of time, says Weber.
Measurement times are only reconstructed
A player can move several decimeters between two sampling times (frames). The central problem is that the player positions are not measured directly at the exact decision time, but are reconstructed between measurement times. Such an interpolation (mathematical process for estimating unknown values) only approximates the actual movement in football.
“They have a huge measurement inaccuracy and still make decisions that are in the range of millimeters or centimeters. That makes no sense to me.”
Space scientist Dr. Tobias Weber
Players do not move at a constant speed like linear objects, but rather demonstrate highly dynamic acceleration, deceleration and rotation maneuvers.
Semi-automatic work technology has been used in the “Kölner Keller” since this season.
In addition, extremities can reach significantly higher speeds during tackles, shots or clearing actions than the player’s pure running speed. Especially in these non-linear, highly dynamic movement phases, a significant source of uncertainty arises in position reconstruction and contributes to the considerable measurement inaccuracy.
“Invisible space” of up to 60 centimeters?
If a player runs at 35 km/h and is filmed with the cameras currently in use, he moves around 19 centimeters between two frames. In extreme cases, the defender tries to put him offside and runs (also at top speed) in the opposite direction.
Added together, this creates a relative speed of 70 km/h and the “invisible space” between two frames doubles to 38 centimeters. “In the worst case, you can even assume that 60 centimeters of distance will be covered,” says Weber.
Weber: “Illusion of accuracy”
Since football is a dynamic game with lots of accelerations, stopping maneuvers and rotations, there would hardly be any uniform movement. In some scenes, arms or legs are accelerated up to 100 km/h. The measurement inaccuracy then becomes even greater. When the ball is played, the position of the players cannot be observed as precisely with the existing technology as suggested by the TV animations. Weber speaks of an “illusion of accuracy.”
Semi-automatic offside technology in the “Kölner Keller”
An AI in the background automatically sets the offside line.
However, the DFB and DFL seem to be aware of this problem. Visit to the “Cologne Cellar” with VAR boss Dr. Jochen Drees: The semi-automatic offside line has been used here since this season. Away from the manual process – towards a technical solution. The goal: to speed up the decision-making process. “A system in the background is now helping us,” says Drees.
An AI records player and ball positions. A possible offside position is quickly recognized by the system. “At that moment we no longer have to create a line, we no longer have to specify a playback period, but the system suggests these components to us,” explains Drees. At the end, the video referees just approve these suggested lines. Incidentally, the referees in the “Kölner Keller” do not see the animation with the player models.
Problem: The camera’s low sampling rate
The optical multi-camera player tracking system TRACAB from the Swedish company ChronHego is used in the Bundesliga stadiums. There is an acceleration sensor built into the game ball that works with a sampling rate of around 500 Hz, but the player tracking only works with a sampling rate ten times lower (50 Hz). The system has been certified by FIFA.
Drees admits: “We know that every technology we use naturally has a certain tolerance built into the system, because the technology can only measure this to a certain extent.” In other words: Space scientist Weber isn’t entirely wrong with his calculations.
Automatic offside detection at the World Cup in the summer
FIFA President Gianni Infantino wants to set new technological standards at the World Cup.
At the World Cup in the summer, FIFA President Gianni Infantino wants to set new standards in offside technology: completely automatic offside detection will be used there. To do this, all players from all countries are scanned in advance in order to create lifelike avatars. Away from the model – towards a 1:1 image that comes very close to the original.
Weber is still skeptical: “Even in such small spaces, like here in the Columbus module, we know that we have measurement inaccuracies if we try to detect the bodies without markers. And they won’t be able to do this on an entire football field until the summer, when we will be confronted with the illusion of accuracy again,” he suspects.
Premier League role model? Or Canada?
But how do you get the problem under control? The issue of offside is handled differently in international football. Since this season, for example, the English Premier League has introduced a tolerance range of five centimeters. Alone, mind you. Drees emphasizes that this is currently not an option for the Bundesliga.
A different model is currently being tested in the Canadian Premier League, suggested by coaching legend Arsène Wenger. In the so-called “daylight offside” the striker must stand with his entire body closer to the goal line than the defender and there must be a free space between the attacker and defender where “daylight” shines through. A model designed “per attacker”. FIFA wants to make the game even more attractive and expects more hits and more chances to score.
Football soon without linesmen?
The technology is getting better and better – that’s clear. The question will be how much the systems can be upgraded in the future. Drees is convinced that the technology used will continue to improve. Then the measurements could become even more precise and football could continue to change. “Maybe at some point we’ll have two or three referees running on the field. Like in handball or basketball. And these black-and-white situations that we can represent will actually be made available to the referees via technology,” says Drees.
People remain an important factor
The scientist Weber would take a different approach to the topic of offside in the future and would again pay more attention to the human factor. “When we interact with our crew, we trust primarily the astronaut, not the sensor. It can always break. Our most important feedback comes from people and not from technology.”
