28 April 2021
Can we (always) trust technology providers?
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The offside rule has been part of the Laws of the game since the very start of football. Originally, it was used to give more or less benefits to the attackers / defenders.
Nowadays, it is still an interesting and challenging issue, in particular because FIFA is now considering to introduce a (semi)-automatic offside decision making technology. For the following reasons, we question if technology can (always) provide a solution as they pretend.
The last 20 years, Werner Helsen's research group has been involved quite intensively with offside research. We even developed our own software to precisely detect offside in TV footage because of parallax errors. Based on these experiences, below I provide you food for thought.
The most important limitation is the frame selection. Even in the Champions League, there is only a sampling rate of 50 Hz. There are cameras filming at 150 Hz but this is just for high definition slow motion. This means 0.02 seconds between 2 frames. A player running at 25 km/h covers 13,88 cm. This can be the difference between onside and offside. As a result, this margin of error needs to be considered to detect ‘real’ offsides, because everything below is questionable.
Another limitation is the offside line that is 5 cm wide. If there is overlap between the lines of the second defender and the attacker, then technology cannot provide any accuracy. In this case, what is the best option? Give the benefit to the decision of the AR on the field? Or give the advantage to the attacker? In the Champions League there was only one such a situation, but in the Premier League there were 8 last season. In this case, technology cannot help and it is misleading to pretend that it is an accurate call.
As sport scientists, it is important to consider this margin of error. A margin of error is also considered for goal posts. FIFA accepts a 20 mm deviation per meter. At the top of the goal this can be 4 cm, which is a lot.
Therefore, the current offside rule is too complex and the margin of error too big (in combination with the importance of it and the time it takes to draw the lines). At the beginning of the VAR system, the idea was to reduce the human error, but now the wrong impression is provided as if the technology works perfectly but this is certainly not so. The time it takes and the frustration it creates may question the VAR system which is very unfortunate.
Therefore, we need to think of solutions. Some people say to only look at the feet but this does not solve the accuracy problem. Therefore, another solution may be to decide about offside if there is no overlap at all between the attacker and the second last defender. A while ago, they called it daylight in England. This idea was not fully the same, it could be easier and clearer to detect offside, even for the human eyes of the ARs. It would also lead to less discussions.
Last but not least, it would benefit the attackers and would certainly result in more goals!
Food 4 thought.
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