Raheem Sterling and the history of measurement
How certain can we be about close offside calls?
We take rulers, clocks and thermometers for granted, but the history of these inventions is anything but straightforward.
In 1792, Pierre Méchain and Jean Baptiste Joseph Delambre set out to establish the metre by measuring the distance between Dunkirk and Barcelona. In 1772, Jean-André de Luc wanted to establish the temperature at which water boiled. To do so, he needed a sample of water with no air in it, and so he walked around for four weeks straight shaking a flask of water to expel all the air from it. John Harrison spent most of the 1740s grinding ever more precise metal wheels to make his watches work.
I often wonder what these men’s friends and families thought of their obsessions. But of course, from a distance, we can appreciate their visions because we depend on them to tell the time, to boil a kettle, to make journeys, and of course to work out whether Raheem Sterling is offside or not.
The first VAR offside controversy in the Premier League was in the very first match it was used in the Premier League: West Ham vs Manchester City in August 2019. I was at this match but, as is typically the case with VAR, it was only when I got home later and watched the highlights that I realised what had happened.
City had played a very slick and fast passing move, with David Silva flicking the ball on to Raheem Sterling, who then squared it for Gabriel Jesus to score. However, the VAR replay showed that when Silva played his pass, Sterling was fractionally offside, and the goal was disallowed.
To decide whether he was offside or not, the referee froze the video replay at the moment the ball was played to Sterling. This is the moment, on the replay, that David Silva's boot first makes contact with the ball. At this point, Sterling was deemed to be offside.
The relevant measurement issue is that we can't be totally sure at what point David Silva did first touch the ball. The footage used by the referees takes 50 frames per second: that is, one frame every 0.02 seconds. The referee has to pause the footage on the first frame that shows Silva's boot hitting the ball, but in reality, Silva's boot might have hit the ball somewhere in between two frames.
Raheem Sterling is very quick. His top speed is just over 20mph. He wasn't going at top speed for this goal - let's say he was going at just 10mph. That's about 4.5 metres per second, which is about 9 centimetres every 0.02 seconds. So in our 0.02 seconds of uncertainty, where we are not sure if Silva has touched the ball or not, Sterling has moved about 9 centimetres. And yet he was deemed to have been offside by 2.4 centimetres.
Hypothetically, this situation could be even worse. Imagine a situation where an extremely quick defender and attacker are both moving at top speed in opposite directions. In this case, in our 0.02 second window of uncertainty the defender is moving about 18 centimetres in one direction and the attacker 18 centimetres in the other.
The obvious riposte to all of these measurement issues is: what would you do instead? No measurement on earth is completely accurate. All measurements have some error. The reason VAR was introduced was because the error made by humans judging using the naked eye were very much greater than +/- 9 centimetres. Back in the 2013-14 season, when Raheem Sterling was playing for Liverpool against Manchester City, he had a goal ruled out for offside despite replays showing daylight in between him and the last defender.
Ultimately, the offside rule is fiendishly difficult to measure. It was first introduced in the 1860s when we had far fewer sophisticated measuring tools than today; in fact, the offside rule is about a decade older than the international agreement that defined the metre.
But what we can see with offside, as in many other fields of measurement, is that as your measurement tools get more accurate, they make the remaining inaccuracies even more noticeable. The quest for greater accuracy often ends not with perfect accuracy, but with a resigned acceptance of uncertainty. Was Sterling onside or offside when Silva played the ball? We will never know for sure.