- Podcasts
- The Naked Scientists
- Fever pitch: the science of the Football World Cup
STADIUM.jpg
Share
The FIFA World Cup is taking place across the United States, Canada, and Mexico. It’s often called the beautiful game, but is it really more science than art? This episode features Rachael Ralph, Hugh Hunt, and Alex Grantham on the physics of football; Tom Brownlee on elite player performance; Gill Cook on the psychology of fans; and Jan Wendt on whether AI can assemble a top squad.
In this episode
00:46 - Is football just physics?
Is football just physics?
Hugh Hunt, engineer, and Alex Grantham, goalkeeper
The first tri-nation FIFA World Cup is getting underway in Canada, Mexico and the USA, where 48 teams will play 104 matches to be crowned the greatest international side on the planet. Argentina are hoping to retain the trophy they lifted in Qatar in 2022 after a dramatic penalty shootout - but the bookmakers have France and Spain as this year’s favourites. But today, we are exploring the science, technology, physiology, and fan psychology that underpins this global showpiece, and we begin with Rachael Ralph who has been visiting what is arguably the birthplace of modern football…
Rachael - I'm standing at Parker's Piece in Cambridge. Next to me is a football monument titled '1848 Cambridge rules', a memorial to the 11 rules written by the students of Cambridge that year to unify the game. However, it wasn't until 1863 that a group of representatives came together to lay down the original 14 rules of association football. 160 years on, football has developed into the most popular - and lucrative - sport in the world, with the World Cup being reportedly watched by more people than any other sporting event. But what is football without the famous ball itself? With me now are Hugh Hunt, a professor of engineering at the University of Cambridge, and Alex Grantham, a former Oxford City goalkeeper, to help explain the physics of the most recognisable ball in global sport.
So is it true that you can kick a football further than you can throw it?
Hugh - I reckon you probably can kick a football further than you throw because your leg is longer than your arm, so you probably get more speed out of your leg. What do you reckon Alex?
Alex - If I want to get the distance, ball's down, and I need to get it to a player over the halfway line, fastest will definitely be to kick. Only reason I wouldn't, is if the ball was in my hands already.
Hugh - But I mean we're just over the road here is Fenner's cricket ground. I reckon if it came to a cricket ball, you wouldn't want to kick a cricket ball, but if you had a cricket ball, I reckon you could throw a cricket ball further than you could kick a football.
Alex - I may not be an expert in physics, but I can confirm I would not kick a cricket ball. I definitely would not want to do that. I think a lot of it must come down to the ball itself.
Rachael - So talking about the physics, we're interested in seeing what happens to the football when you kick it without spin or with spin. So Hugh's gonna kick the football and with our resident goalkeeper he's gonna try save the ball, but firstly Hugh's gonna kick it straight without any spin and we're gonna see what happens.
[football kicking sound]
Hugh - Oh that was lucky! Yeah, so that was that was pretty straight, and well you just didn't have to move did you? And it kind of goes straight, not spinning. It curves through the air because of gravity, but doesn't curve left or right.
Rachael - What actually happens around the ball as you kick it straight?
Hugh - So as the ball moves through the air, the air is going around each side sort of equally. So you can kind of think that the air will push the ball around, but if it's pushing it left and right equally then the ball will go straight.
Rachael - Should we see what happens when you add a bit more spin to the ball. [football kicking sound]. That was pretty straight again!
Hugh - I did my best. I've got an idea. Let's swap roles. Alex who can spin a ball, and he can kick it to me.
Rachael - Yeah that's a good idea![football kicking sound]. Wow that was a good save! Oh almost hit a cyclist!
Alex - It had a lot of shape. I didn't really think how much power I'd put on it, but he did get to the ball and that's what matters. What you definitely say is a right-footed player like myself will get more right to left curve naturally when you kick the ball and you're putting more spin on the right hand side of the ball, versus a left-footed player who would have the opposite effect on the other side. So for the left curve I'll be using my left foot.
[football kicking sound]
Rachael - Hugh was nowhere near that. That was a lot of spin.
Hugh - He might be a professional footballer, but he didn't get that curve!
Rachael - There was some curve on that.
Hugh - There was a bit of curve.
Rachael - So what happened around the ball then to get the curve on that?
Hugh - Right, well if you've got a ball which is spinning as it moves through the air, then the air kind of likes to stick to the ball and if the ball is spinning, then the air will be dragged around the ball in one direction and that kind of throws the air off to the left if the ball is moving to the right. And it's kind of like Newton's third law, every action has an equal and opposite reaction, that if the air is swung around in one direction the ball has got to move in the other direction.
Rachael - And is there a name for this effect?
Hugh - Yeah, it's called the Magnus effect, a bit like Magnum ice creams, but I think I'd prefer the Magnum.
Alex - And when it comes to the backspin, that's actually quite useful in football when you're trying to put the ball over the top but you don't want it to run over and out of play. You will get under the ball just to give it a bit of backspin so that it just sits nicely once it goes over.
Hugh - One of the things about spin is it's not only the spin through the air that matters, but when the ball hits the ground, if it's really spinning, it can move left or right or forwards and backwards on the ground. And also, if it hits the crossbar when it's spinning then funny things happen. Now, you may remember the Frank Lampard disallowed goal.
Alex - I certainly do, certainly do!
Hugh - So what happened was that the ball hit the crossbar, and started spinning, it went over the goal line, it came back up and hit the crossbar again, and came out. And the only reason it came out was because of how much spin it had got from having hit the crossbar. And if it wasn't for the spin, the ball would have hit the crossbar, gone, bounced in, and carried on and hit the net. So it's the spin that brought it out again.
Alex - So it's physics fault, it's physics fault that England got knocked out of the World Cup.
Hugh - Physics fault.
Alex - You heard it here first.
Hugh - And it was amazing just how much column inches there was in the newspaper the next day, and there wasn't one mention of angular momentum!
Rachael - So in terms of the curve of the ball, can you add more of a curve or less of a curve depending on speed, for example, or the weight of the ball? And I know in golf, the air temperature does have quite a big effect on how far the ball actually goes. Does that have an effect on football as well?
Hugh - Well, so air density is affected by temperature, and by air pressure, and humidity, and things like that. The denser the air is, then the more the curve will be, and you have to have, to get curve on a ball, you have to have forward speed and spin, and then lightweight balls will curve much more easily than heavy balls. I've got a lightweight ball here. Alex can have a go at this. I've got a lightweight ball. Okay, give that a kick.
Alex - This is completely different. It just gets caught in the wind. Interesting, it doesn't go with much distance at all. You'll put the same amount of power into the heavy ball as this light ball, and the light ball will probably go about a third of the distance, but in a huge different angle.
Hugh - Yeah, so the weight of the ball matters, and I mean, in the old days when they had leather balls, the balls on a rainy, wet day, they'd get really heavy. Must've been quite hard to curve them.
Alex - Yes, and to head them especially. I definitely wouldn't recommend that once it's soaked up all the water. I will say a lightweight ball when you're playing is very noticeable and it's an absolute pet peeve of mine because they change balls per tournament. So, for example, in the FA Cup, we were playing with a different ball than we would in a national league competition, and teams often choose to train with that ball because it moves and interacts in such a different way.
Rachael - Alex, as a goalkeeper, when people are taking a free kick, what goes through your mind? Because obviously the ball could go in any direction with all this spin that we've been talking about. So what are you thinking when you're facing this free kick?
Alex - Angles play a huge part and it's all subconscious. I'm not going to pretend that every goalkeeper is a master of physics, but you are looking at how they can get that ball up and down over your wall. You're also looking if they're a right or a left footer, then they're more likely to put curl on in one direction or another. So you have to position your wall in a way that prevents them to getting it up and down and around.
Rachael - And finally, the most important question, is it coming home? Is football coming home?
Alex - Football is coming home. Finally.
Hugh - Well, look, I grew up in Melbourne. I'm pretty sure that it's not coming home.
Alex - We'll bring it on a tour. When we come and play the Ashes, we'll bring it with us, the World Cup, and then you can see it in Australia.
09:30 - Getting a footballer in peak condition
Getting a footballer in peak condition
Tom Brownlee, University of Birmingham
So, we’ve heard about the ball, now let’s look at the other key component in the game: the players. The World Cup, of course, doesn’t begin just with the referee’s whistle but with weeks, months, and years of planning. And something that’s really changed in recent years is the application of data science to match preparedness and fitness. All kinds of metrics are being collected these days, and players are even tracked around the pitch by GPS. The aim is to build a numeric picture of performance to enable coaches to spot and fix problems early and keep their teams in tip top condition. Physiologist Tom Brownlee is a consultant advising on ways to do this, and an assistant professor in applied sport sciences at the University of Birmingham. He's been speaking with Chris Smith...
Tom - Daily monitoring is something which has increased massively over the last 10-15 years. Now, it will take lots of different forms, so you will see them wearing what looks like a sports bra during training, that will be looking at their heart rate, they'll be wearing a GPS unit between their shoulder blades, allowing the coaches to understand exactly how much distance they've covered, how much of that has been at high speed. The twisting and turning has more impact on your muscles and joints, for example, whereas the distance as a whole affects your heart and lungs differently. So that's the kind of movement analysis, I suppose, but they track way more than that. They will do questionnaires when they wake every day, how did you sleep, does anywhere hurt, how up for training are you today. They will also be screened by the physios to see if they've got any strains or anything like that. They will then also have performance testing, which they won't do necessarily every single day, but they might do jump testing, and that allows us to understand neuromuscularly, so how their nerves and their muscles are firing, and that's not necessarily to say, oh, you're not training today or you're not playing today, but it's to allow that training or match minutes to be optimised so they can get the best out of them.
Chris - Do we know how to interpret all this digital data though? Because, for instance, if you had just GPS data showing movement around a pitch, a goalkeeper's going to look like they haven't gone anywhere, versus someone who's a midfielder who's been everywhere. So do we actually understand how to interpret the data, and do we understand how to relate it to an individual player? Because different people are going to have different physiologies, they're going to have different strengths, they're going to have different capacities to take this kind of treatment, and some are going to fare better than others. So do we have a standard set of data for a player, and therefore we know when they're operating inside their comfort zone and when things are slipping?
Tom - When this kind of data analysis started sort of 10 or 15 years ago, it was quite standardised because we didn't really have much more that we can use. Thankfully, now it's become a lot more individualised for the reasons that you speak about the positional demands are so different, even the role specific to the position that you play or how the manager wants you to play. It's much more individualised now and we've been able to become much more specific in how we look at those numbers.
Chris - Are there numbers that are giveaways that a person is in the sweet spot for they're as fit as they can be, they're as ready as they can be, they're as well nourished as they can be? Are those sorts of things being looked at and is that the sort of thing that people are seeking to optimise? And can you also tell when someone is slipping a bit, you think we need to help them in a particular area or rest them up a bit. Are people responding to data in that sort of way now with their players?
Tom - One of the key GPS metrics is something we call high-speed running, which isn't necessarily a sprint but it's a quite a fast jog. So we would have an understanding of what would be typical for a player in a training session of a certain type. So if what you would expect is kind of a sort of plateau, if that does start to dip off it might be something that you might want to look into. It's deviations, it's changes away from that average where you might start to think, oh maybe we should just keep an eye on this person. And thankfully there is a real blend of art and science at the top level, it's not the tail wagging the dog, it's not someone with a white coat saying their number isn't right, they're not playing, but it allows a collage to be built around that individual. So it might just be having a word with them and saying, you feeling all right today? Oh actually I didn't sleep very well last night, my roommate snores all night, and you know it's little things sometimes, it doesn't have to be the baby out with the bathwater. But it can be difficult in tournament football right? Because you also want your best 11 on the pitch. So maybe you think, look I don't think they're quite right, so they're only going to get a half today. That's where that coaching eye comes in, because we're playing at the highest level here aren't we, you want your best team out there.
14:34 - The psychology and impact of football fans
The psychology and impact of football fans
Gillian Cook, Liverpool John Moores University
So far we’ve looked at the science behind the balls and the players, and in a moment we’ll hear how a new AI-based system could turn the game totally upside down. But first, to another critical component of any match - the fans! These diehard supporters are often referred to as the team’s “12th man” - almost an extra player that can help propel a side to victory, intimidate the opposition playing away, or lift a flagging performance. But can a bit of passionate support really make a difference, or is it just hot air? Chris Smith has been speaking with someone who has the answers...
Gillian - So I'm Dr Gillian Cook, I'm a senior lecturer in sport and performance psychology at Liverpool John Moores University and I also work as a sports psychologist with a variety of Olympic, Commonwealth and professional teams including a Scottish Premiership football team and my research predominantly looks at why some athletes can perform with excellence under pressure and others wilt under pressure and then what it is that managers can do to create the conditions for athletes to thrive under pressure.
Chris - A lot of performers say that the crowd's energy gives them energy. I remember interviewing a musician, a very famous musician and he said to me that the crowd make us play the way we play.
Gillian - When you've got a crowd you have energy that comes from and what happens is you've got something called emotional contagion, so our emotions become contagious and if the crowd is particularly rowdy, they're particularly amped up, that then gives that same emotion, that same arousal or energy to the players and they then also play with more motivation, more effort and usually the more effort players play with the better the result tends to be but it can also sometimes go the opposite way. Sometimes fans can make players become very self-conscious because they don't want to let them down and they start to get what's called a fear of failure.
Chris - So there must be two elements of sort of training a player base for this because you've got to help people to have that and harness that winner effect when things are going well the crowd are with you it's going to bolster your performance but then be able to zone that out completely and be really focused on what you're doing when you're doing something specialist like a penalty.
Gillian - We are stressed when we don't think we have the resources to match the demands so the demands of the situation being is there a threat to our ego, do we think we'll win, is there uncertainty and our resources to cope are things such as do we have confidence that we're going to do well, have we done well before, do we do well against this particular team and if we think we are going to do well then having a crowd really boosts performance and when you're playing with more confidence that then you know clearly then creates a better performance outcome and if you feel like you're in more control of the situation so it's our fans we can control what they do again that enhances performance and finally if you see the crowd as how good can we be, what's the possibility, how fun, how great can we create this atmosphere that helps you to perform even better. The flip side in sport is what we call choking so it's when you've got very good players that you expect should perform very well but they don't and that's when they really start to overthink and get into their own head instead of thinking of the possibility what could go well, how good could this be, how many goals could we win by, they start thinking I don't want to lose.
Chris - Is a negative crowd always a bad thing though? Can that sometimes work to your advantage because you think well I'm going to show them especially if it's an away crowd and you expect them to to be anti your side can that sometimes actually rather than diminish a player's standing in their own self-worth can that actually help them to make reverse psychology kick in?
Gillian - It absolutely can so we can see that from a motivational perspective one of the biggest forms of motivation that humans can have is either a sense of injustice or trying to prove people wrong and we can see that when a crowd is particularly hostile that players can then boost in their effort.
Chris – So it is like an U shaped curve then. If the crowd are hostile you can play really well because you want to prove them wrong, if they're really for you, you play well because you want to go with them but there's a sort of a dodgy spot in the middle where it could go either way.
Gillian - There's sort of that optimal in the middle and you don't want too much or too little of something because you can also get over aroused, you can try too hard, you make tackles that are too strong and you end up getting sent off but equally as you say and we saw this during Covid that the one of the biggest things that we can see in sport from an awful lot of research is there is a home advantage. Teams do win more at home when they have their supporters they're in the familiar space and that disappeared in Covid. Covid was the perfect natural experiment where you got rid of the crowd and it was thought to have happened for two reasons. One the emotional contagion of the crowd that then disappeared so players motivation from that those external sources were really reduced that extra energy that you might need in the 83rd minute was reduced but it also had an effect on the referee. We know that from an awful lot of research that referees are more likely to give more yellow cards to the away team. Now why is that? Well firstly referees are working in an imperfect environment they don't have all the information they need and so some of the time they will use the noise of a crowd to gauge whether a foul is particularly bad. The louder the noise the worse that foul is likely to be. Now that clearly isn't always the case but referees do sometimes use that as a cue to work out okay that's a particularly loud noise, I will therefore give a card. And there's also a motivational element particularly when a crowd is closer to the pitch we can find that referees give more cards to to the away team and also more favourable decisions towards the home team for a one can be a motivational reason that you don't want to disappoint and you can also be intimidated by a crowd.
Chris - We've talked very much about sounds when you're a player on the pitch and you see this vast sea of fans the visual must have a huge psychological effect as well especially given how prominent the sense of vision is to a human brain but does the fact that the fans tend to dress in team colours does that make a difference as well so players are basically seeing a sea of red or a sea of blue because we know that colour does appear to influence how we think I mean lots of studies have shown that.
Gillian - Yes it does so we we know from research that the colour red makes you think of aggression and dominance and there's research that shows there was a research study that looked at the Olympic games in 2004 looked at boxing and boxers were assigned red or blue at random and it was found that the boxers that boxed in red were more likely to win than those in in blue and there was a statistically significant effect which shouldn't be the case if the boxers were just assigned colours at random. So why is that so when you're playing in in red as I say you are you're feeling dominant but from an opponent's perspective you see red you see threat and we see that in nature all the time with the as you say with the fans when they're wearing big blocks of colour firstly they stand out think of the Dutch national team they're all in orange firstly it's a colour that takes your attention so it's distracting, can be distracting in a bad way for the players that are playing the Dutch national team seeing a huge block of colour is also intimidating so it can take your focus and that can then help and boost your performance if you're seeing a huge block of orange in a sea of orange that can then help you think if you're a Dutch player I have the crowd behind me the support is willing us on to win let's win for our families the supporters and for our nation.
23:39 - Can AI build the world's best football team?
Can AI build the world's best football team?
Jan Wendt, CEO of PLAIER
One of things that teams invest the most amount of money in is player recruitment. So how might AI help build the best possible team? Jan Wendt is the CEO of PLAIER, an AI-powered scouting platform that scans, analyses, and aggregates the latest available data on footballers with staggering accuracy. He's been telling Chris Smith how it works...
Jan - PLAIER came up as a coincidence because we've developed a very, very powerful AI and no one was giving us data, so we bought football data and the outcome was totally surprising. We were able and we are able to measure a football player's performance very precisely and out of that we can derive the squad strength, the squad strength needed to win a championship and then we can also measure the coach's performance which is another variable in the game.
Chris - When you say data, what data do you train your AI system on?
Jan - The football player is probably the best tracked employee the world has ever seen apart from astronauts and pilots, so there is an enormous amount of data for a football player, there are different types of data. What we are using is the foundation of any football data, it's event data which basically measures the actions of a player on the pitch.
Chris - How do you track a player around a pitch?
Jan - Well, the data providers, they put a scale on the field and a timestamp and then they have about 150 in average per position metrics which they write down or a computer detects it and puts it into a kind of Excel list which is 150 metrics per minute per player per position.
Chris - So there are computer programmes breaking down any football game and they're tracking each player all around the pitch all the time so they know where they went when, how many touches on the ball, who they were near when they were playing in certain positions or executing certain moves and so on.
Jan - Exactly and it goes even beyond that. In England in Premier League you even have mesh data which are 50 virtual body points so you can measure any arm movement, leg movement, head movement within these already named parameters.
Chris - That's extraordinary. So you literally have what a player has done on a minute by minute or second by second analysis across a game.
Jan -Totally crazy, yeah.
Chris - Over how many years have you got this data?
Jan - For the last 14 years.
Chris - Goodness. So, your system now, it ingests all that data so what sorts of questions can you ask of it then?
Jan - How does a single player impact the success of a team? That's the core question.
Chris - But the number of degrees of freedom must be huge because certain players are going to play in different positions, they're going to play in different teams, they're going to play with different teammates and they're going to play against different teams and so surely all of those degrees of freedom, there must be enormous uncertainties.
Jan - No, it's actually we've reached an enormous level of accuracy. So in transfer decisions we have reached 90% accuracy so nine out of transfers are exactly as we predict them. But even more than that, out of these player scores which we've developed, we can even derive the squad strength you need to be successful in the following season. So it goes beyond just having a look at the single player.
Chris - Does this mean then that if a manager comes to you they can say, well this is the lineup I'm thinking of putting on the pitch, these individuals, and these are the positions I'm thinking of deploying them into. Can you sort of gamify that for me or do you turn it round and do you say to them, well if you put this person with this set of teammates in these positions, this is your sweet spot?
Jan - Both ways are possible. So the first part is you give us a squad and S11 or a lineup and we can tell you exactly what the outcome will look like because obviously it depends on the opponents and on the league you're playing in. And the second part is if you turn this around we can give you a very, very clear advice if the players you have selected on your short list or long list or which you are up to transfer, how these players will perform in your team in the following seasons.
Chris - When I was little I used to love football manager type computer games and it was really easy wasn't it because it told you if you bought this player they were really good as a striker, they were rubbish in defence and you effectively have got that then. If you've got this way of assigning parameters to players you effectively can do what those footy manager programmes of the 1980s were doing.
Jan - Exactly. It's a little bit like when you watch old James Bond movies all the stuff they were using trackers and all this stuff is now on a mobile phone and this football example of the football game itself is the same. The future is there now.
Chris - Does this mean though that if you analyse a player you can spot where their weaknesses are and so then you can say well this is what you need to work on. When this happens you tend to do this, a bit like with a car racing you could look at when a certain set of manoeuvres is executed this is tends to go wrong. Can you do that and help players to up their game?
Jan - That is an interesting question. We don't know to be really honest because we haven't come that far. We are in step one of the game still which means we still have to persuade clubs to use us more as a validation tool in this very first phase of AI usage in football. Now in a second step that would be interesting to see if you can work on your strengths and weaknesses. This is something we have to figure out.
Chris - One way to validate platforms like this is that you train it on a set of data from previous years and then you get it to make predictions about a year that you do have the data for but it hasn't seen it yet to see if it agrees with what actually happened. So if you do that how good is your system?
Jan - 91% accuracy on transfers.
Chris - What does that mean? What do you mean by inaccuracy on a transfer?
Jan - Okay so right now the accuracy of a transfer like if a player really makes an impact a positive impact on the team right now as an average figure is about 40% so 40% of all the transfers work the way the human responsible was planning it to happen and we bring it up to 91% so almost every transfer works as predicted and on a league prediction on the bigger leagues or the for example the top five leagues in Europe we are in the prediction of the season results we are plus minus one rank and plus minus four points precise as of today but now obviously we're getting better and better so that's the you know as of today and this accuracy will go up in the years to come.
Chris - Who do you think then are going to be the two teams in the final for the World Cup?
Jan - Oh that's I think you don't really need AI for that. First of all competitions are have a different mode because the low outcome game football produces a lot of you know you can be the pressing team you can have 10 expected goals in the end the other team scores once and win the game so a cup competition is a different thing but I would say the typical outcome would be among France, Argentina, Spain and England that's for that these are the four strongest squads and they should make it obviously depending on the draw and all the other circumstances which we can't foresee but that should be the semi-final.
Chris - And who's going to win?
Jan -I don't know that's really difficult because as I said you know they're not as strong in a cup competition in a league the best combination wins but in the cup competition being lucky or being unlucky has a great impact so my personal recommendation is France but as I said all four teams can make it.
Related Content
Blessed Algorithms
Low frequency bass boosts boogieing
….And S T R E T C H
Oscars predictable as ever; in fact moreso...
QotW: how do zip files work?
- Previous Why does a slice of toast land butter side down?
- Next Why does a slice of toast land butter side down?
Subscribe for free
Support Us!
Forum discussions
Featured
- Load more
Source: The Naked Scientists
