xG And Analytics Under Amorim

[quadrant]

All depends on your tactics/how you train - this is the big limitation of xG and why it's good to look at trends over a season and not really as something to hone in on to make/break an argument.

Dont quite follow, praps you could expand?

 

[tomaldinho1]

Actually it shows Arsenal have better finishers than us and also have not been a great attacking side this season as they were last season.

It doesn't necessarily 'show' either, you have to understand the stat.

For example, very quick exercise using understat, look at where United vs Arsenal shoot from. If one team is purposefully having less shots from outside the area and more from within the six yard box, how much of that is finishing versus tactics? How much is simply bad decision making?

Also just using a bit of context on the second part, pre Saka injury Arsenal were top of the league for xG and xPoints, Jesus then got injured, Havertz followed, and Martinelli was out for a few games. Would we not expect their xG to then drop off (that is their entire starting front 3 out at the same time for 10+ games) considerably?

 

[Chipper]

All depends on your tactics/how you train - this is the big limitation of xG and why it's good to look at trends over a season and not really as something to hone in on to make/break an argument.

I'm beginning to think that xG overvalues/undervalues certain types of chances to an extent even though it comes as a reasonably decent model overall.

The better chances slightly undervalued, the lesser chances overvalued. Could well be player dependent though.


Edit: Would require a deep delve, but a player like Semenyo is well known for taking lots of low xG shots and he is underperforminh his xG, Eze very much in the same boat now. Wissa, Haaland, Isak, Brennan Johnson with some of the highest xG's per shot and have overperformed or come out around even. There are counter examples too that would go against that narrative, so like I say would take a deep dive.

Team-wise suppose you could at look at Forest and how they've conceded fewer goals than their xG against. They have the lowest xG per chance against them so could be a factor. When it comes to non-penalty xG per shot taken, the best 3 are Brentford, Liverpool and Newcastle, and they have all scored more than their xG.

The players on the end of the chances count too, but maybe the modelling is slightly off as well.

 

[Cassidy]

It doesn't necessarily 'show' either, you have to understand the stat.

For example, very quick exercise using understat, look at where United vs Arsenal shoot from. If one team is purposefully having less shots from outside the area and more from within the six yard box, how much of that is finishing versus tactics? How much is simply bad decision making?

Also just using a bit of context on the second part, pre Saka injury Arsenal were top of the league for xG and xPoints, Jesus then got injured, Havertz followed, and Martinelli was out for a few games. Would we not expect their xG to then drop off (that is their entire starting front 3 out at the same time for 10+ games) considerably?

The last paragraph yes hence why they have not been as good as last season as an attacking side which is reflected by the xG.

 

[tomaldinho1]

Dont quite follow, praps you could expand?

I hope this makes sense.

Chris Wood is massively overperforming his xG this season, the quick response people will have is that he is a 'good' finisher but it's really not that simple.

xG on an individual level is quite good, in my opinion, with a bit of extra context alongside it. In Wood's case, you can make a strong argument to say that, compared to the historical data, Wood is elite at finishing a certain, quite specific, type of chance looking at his goal map (right footed or headed finish from left of centre, close to GK. I think he has one goal which bucks this trend and was a long shot vs Palace and terrible keeping).

xG on a team level however is not great if you try and use it as some have above. Forest get battered on xG in many games and, if you only looked at xG and nothing else, you would believe they had the most insane luck both in terms of somehow not conceding but also scoring, the truth is simply they plan to play in a certain way. I imagine as @Chipper says you can't really escape from the fact that every shot on a football pitch is completely player dependent (in fact every action must be) and then the frequency/type of shot will mostly be down to the tactical battle between both teams.

For example, Forest go a goal up, they might sit in even more and shut down the one or two players they deem the greatest threat. The opponent will keep creating half chances given they are sitting in and their xG will keep rising but the context of who is shooting is not part of the calculation. At the end of the game it will seem like Forest got super lucky, but actually they played for that exact scenario. Just thinking of this alone, you can see how warped xG at a team level becomes over 38 games with near countless variables in every game of football (cards, injuries, weather, pitch sizes, the list is near endless).

For me, it is becoming a great stat to use individually alongside others (for example who is actually the best all round penalty box finisher in the league, you could work out every season with a decent amount of accuracy) and a cool way to look at a broad overview once a season is done, but it's very hard to accurately compare two teams solely using xG.

 

[TheRedDevil'sAdvocate]

As far as Forest are concerned, some of the free models, like Understat, actually indicate that they have been over-performing both their xG and xGA when their games are level. Additionally, they have been over-performing their xG most between 1–15 minutes, and their xGA between 16–45 minutes. Which, of course, could be a huge factor to them being able to play "their game". They have spent fewer minutes behind in games than City. Don't call it "luck" if you don't, but you wouldn't expect it to continue next season. Good for them, if it does.

 

[ScholesBrain]

You can never outperform xG with a bunch of poor finishers with no striker instinct.

 

[Chipper]

As far as Forest are concerned, some of the free models, like Understat, actually indicate that they have been over-performing both their xG and xGA when their games are level. Additionally, they have been over-performing their xG most between 1–15 minutes, and their xGA between 16–45 minutes. Which, of course, could be a huge factor to them being able to play "their game". They have spent fewer minutes behind in games than City. Don't call it "luck" if you don't, but you wouldn't expect it to continue next season. Good for them, if it does.

They're certainly overachieving on the 2 expected points tables I'm aware of which has them in 13th and 14th. With negative "luck" (think I prefer variance) they might well be lower than that if the models are correct.

Said in another thread that any downturn is likely to be blamed on Europe next season, when they could play exactly the same way as they have this and suffer one anyway should the models be right.

Throw in those European demands and a key player in Chris Wood a year older and I might even be looking at the relegation odds for them over the summer. Do I think they'll go down? No, but if the odds are big enough any bet can be tempting.

I know I said that they might be doing something that the models don't quite pick up accurately in my last post, but that's not a definite.

 

[quadrant]

I hope this makes sense.

Chris Wood is massively overperforming his xG this season, the quick response people will have is that he is a 'good' finisher but it's really not that simple.

xG on an individual level is quite good, in my opinion, with a bit of extra context alongside it. In Wood's case, you can make a strong argument to say that, compared to the historical data, Wood is elite at finishing a certain, quite specific, type of chance looking at his goal map (right footed or headed finish from left of centre, close to GK. I think he has one goal which bucks this trend and was a long shot vs Palace and terrible keeping).

xG on a team level however is not great if you try and use it as some have above. Forest get battered on xG in many games and, if you only looked at xG and nothing else, you would believe they had the most insane luck both in terms of somehow not conceding but also scoring, the truth is simply they plan to play in a certain way. I imagine as @Chipper says you can't really escape from the fact that every shot on a football pitch is completely player dependent (in fact every action must be) and then the frequency/type of shot will mostly be down to the tactical battle between both teams.

For example, Forest go a goal up, they might sit in even more and shut down the one or two players they deem the greatest threat. The opponent will keep creating half chances given they are sitting in and their xG will keep rising but the context of who is shooting is not part of the calculation. At the end of the game it will seem like Forest got super lucky, but actually they played for that exact scenario. Just thinking of this alone, you can see how warped xG at a team level becomes over 38 games with near countless variables in every game of football (cards, injuries, weather, pitch sizes, the list is near endless).

For me, it is becoming a great stat to use individually alongside others (for example who is actually the best all round penalty box finisher in the league, you could work out every season with a decent amount of accuracy) and a cool way to look at a broad overview once a season is done, but it's very hard to accurately compare two teams solely using xG.

If I understand your argument correctly, you're saying that good teams make chances that suit their players, which means they're more likely to finish them? And they defend by making their opponents attack in ways that don't suit them, eg by forcing teams to cross into the box when they have tiny strikers?

So immediately I'd point out that you're conflating two different things here - your xG (chances), and whether you over or under-perform it (finishing). Those are different metrics. There isn't really a strong correlation between the two metrics, so I don't think you can make conclusions about xG based on whether you're over or under-performing it.

If you rank the current table on xG, its very similar to the current table. Top 5 the same group, bottom 3 the same group, just a few notable changes, like Spurs & Forest almost swapping places. However if you rank the table by over/under-performance against xG, totally different. Forest, Wolves, Arsenal, Newcastle and Spurs are the top 5. Liverpool are 7th, City 8th and Chelsea 15th. If xG and over-performing it were synonymous you'd expect to see a clear correlation between the best teams and the greatest over performance. Liverpool have been a very balanced and consistent side this season, with a style of play that presumably matches their players, since they've done so well. Yet they're not near the top in terms of overperforming xG.

So while I understand your argument and can see merit in thinking it through, the examples you gave don't support the premise. Fundamentally, xG is about chance creation, not finishing, and stats show strong correlation between xG and good a team's attack is. So that's what you'd need to address.

 

[tomaldinho1]

If I understand your argument correctly, you're saying that good teams make chances that suit their players, which means they're more likely to finish them? And they defend by making their opponents attack in ways that don't suit them, eg by forcing teams to cross into the box when they have tiny strikers?

So immediately I'd point out that you're conflating two different things here - your xG (chances), and whether you over or under-perform it (finishing). Those are different metrics. There isn't really a strong correlation between the two metrics, so I don't think you can make conclusions about xG based on whether you're over or under-performing it.

If you rank the current table on xG, its very similar to the current table. Top 5 the same group, bottom 3 the same group, just a few notable changes, like Spurs & Forest almost swapping places. However if you rank the table by over/under-performance against xG, totally different. Forest, Wolves, Arsenal, Newcastle and Spurs are the top 5. Liverpool are 7th, City 8th and Chelsea 15th. If xG and over-performing it were synonymous you'd expect to see a clear correlation between the best teams and the greatest over performance. Liverpool have been a very balanced and consistent side this season, with a style of play that presumably matches their players, since they've done so well. Yet they're not near the top in terms of overperforming xG.

So while I understand your argument and can see merit in thinking it through, the examples you gave don't support the premise. Fundamentally, xG is about chance creation, not finishing, and stats show strong correlation between xG and good a team's attack is. So that's what you'd need to address.

Not really, I gave an example of why xG on a team level is somewhat useless on its own + gave an example of how it can be useful on an individual level.

The point was more that there's a lot more nuance than a team having better finishers or attackers because how much is tactical, how much is luck, how much is individual? You can't use xG in isolation as proof, you have to dig into it.

I assume you mean xPoints, not xG (as the table shifts more on xG)? As said, I think on a team level it is a good overview when you zoom out and use it as you just did i.e. over a long period. I'm not sure how you have come to the bolded? Forest were just an example as they have a distinct style.

Re your point about chance creation, that is a given where does it say otherwise? The point was simply the chance value will not take into account the person who is taking the shot when xG is calculated at the end of the game and, subsequently, added up in the xG league table so maybe you have misread or I have not explained it properly.

 

[quadrant]

Not really, I gave an example of why xG on a team level is somewhat useless on its own + gave an example of how it can be useful on an individual level.

The point was more that there's a lot more nuance than a team having better finishers or attackers because how much is tactical, how much is luck, how much is individual? You can't use xG in isolation as proof, you have to dig into it.

I assume you mean xPoints, not xG (as the table shifts more on xG)? As said, I think on a team level it is a good overview when you zoom out and use it as you just did i.e. over a long period. I'm not sure how you have come to the bolded? Forest were just an example as they have a distinct style.

Re your point about chance creation, that is a given where does it say otherwise? The point was simply the chance value will not take into account the person who is taking the shot when xG is calculated at the end of the game and, subsequently, added up in the xG league table so maybe you have misread or I have not explained it properly.

No, the example you gave was about over- or under-performing xG (or GF-xG if you prefer), not xG. They're different things. You talked about Chris Woods this season looking elite. Chris Woods has 11 xG this season, sandwiched between Raul Jimanez and Evanilson. There is nothing elite about his xG. What's impressive is his over-performance against xG, ie how many more goals he scores than you would expect based on his xG, which is the highest in the league.

But as I pointed out, extrapolating the effectiveness of xG from over-performance of xG doesn't work. There's little correlation between the two.

 

[TheRedDevil'sAdvocate]

They're certainly overachieving on the 2 expected points tables I'm aware of which has them in 13th and 14th. With negative "luck" (think I prefer variance) they might well be lower than that if the models are correct.

Said in another thread that any downturn is likely to be blamed on Europe next season, when they could play exactly the same way as they have this and suffer one anyway should the models be right.

Throw in those European demands and a key player in Chris Wood a year older and I might even be looking at the relegation odds for them over the summer. Do I think they'll go down? No, but if the odds are big enough any bet can be tempting.

For me, it shows that a bit of good fortune in team sports can help you build momentum, and a bit of momentum can raise your confidence. It might continue next season, the underlying metrics aren't predictors, just "pictures" of certain time periods.

On a more general level, what they "show" is that "the table doesn't lie" is one of football's worse clichés. Of course, it does. Leicester weren't an 80-points side in 2015/16. NF aren't really top-5 quality this season. Conte's Chelsea finishing 90+ points was a massive over-performance. United's 81-points season was the same. Klopp's biggest achievement is that he actually turned Liverpool from a team that needed to massively over-perform to compete with City to a team "deserving" of their tallies. And now, Slot is enjoying the fruits of that.

Teams and reporters can pay and gain access to much more detailed stats than the ones available to us. We're trying to get the bigger picture from glimpses, and often enough we get things wrong. But, from my experience, what most people "rebel against" when it comes to the underlying stats is that said stats often challenge "long-held truths". See the discussions on this forum about the "transformative" striker or the "clown" Onana. xG won't tell you that new additions won't improve us. Titles have been won by great footballers playing out of their skins. It would tell you, though, that, in our current predicament, it will most likely be a short-lived joy. The most prolific goalscorers are also the ones who miss big chances more than anyone else. Ronaldo's career xG matches his actual goals. That's why a team's total xG, as a single number, matters. You want to score more goals? Find ways to increase your xG, don't look for "good finishers". Mourinho's second place was, more or less, the product of De Gea having his last truly world-class season at club level. But you can't expect to go far with that. When you concede about 1.50 xGA per game, you need more than a goalie doing crazy stuff to improve your defence.

 

[tomaldinho1]

No, the example you gave was about over- or under-performing xG (or GF-xG if you prefer), not xG. They're different things. You talked about Chris Woods this season looking elite. Chris Woods has 11 xG this season, sandwiched between Raul Jimanez and Evanilson. There is nothing elite about his xG. What's impressive is his over-performance against xG, ie how many more goals he scores than you would expect based on his xG, which is the highest in the league.

But as I pointed out, extrapolating the effectiveness of xG from over-performance of xG doesn't work. There's little correlation between the two.

Please reread what I said and rephrase the question as something is getting lost here. I wrote about xG and two aspects of it, the individual (you are now taking about) vs the team.

 

[quadrant]

Please reread what I said and rephrase the question as something is getting lost here. I wrote about xG and two aspects of it, the individual (you are now taking about) vs the team.

I read it very carefully, but Im evidently not getting something. What are the "two aspects" of xG?

 

[tomaldinho1]

I read it very carefully, but Im evidently not getting something. What are the "two aspects" of xG?

Using it to assess an individual player vs a team.

 

[quadrant]

Using it to assess an individual player vs a team.

Ok, well that much I get. But when you said

Spoiler

xG on an individual level is quite good, in my opinion, with a bit of extra context alongside it. In Wood's case, you can make a strong argument to say that, compared to the historical data, Wood is elite at finishing a certain, quite specific, type of chance looking at his goal map (right footed or headed finish from left of centre, close to GK. I think he has one goal which bucks this trend and was a long shot vs Palace and terrible keeping).

This is about finishing is not?

 

[Ekeke]

We're 6th in terms of xGA, 10th in xG, and no one in the league bar Southampton underperforms their xG worse than us.

I'd be curious to know the breakdown of this for ETH's part of the season and Ruben's, I do remember Bruno and co squandering loads of chances in the first 7-8 matches to really create a disaster environment.

There are loads of issues with the team, but Ruben has halted the kamikaze football Erik went with and solidified the team somewhat, while he still has to contend with the same blunt attack. We probably need three new attackers, two of whom going straight into the first XI.

I think this season ETH had already greatly improved our defense. Remember last season at one point we were averaging 20 shots against us. We ended the season at 17.6 shots against us which was 2nd most in the league to Sheffield United with 17.8. So we were right there as the worst in the league at stopping the opposition shooting.

This season iirc it was down a few, lets say 13-14 and today its 11.1 which is 5th in the league after Arsenal, Liverpool, City and Chelsea

ETH's problem was similar to Amorim's problem. Our attacking players couldnt create lots of clear chances and the clear chances we hdid have our players were finishing poorly. In between we had Ruud, and for his games we were finishing better. Then Amorim came and its been the same problem.

We have the joint 9th amount of shots in the league but 11th most shots on target. So we're poor at getting those shots on target let alone beating a goalkeeper

 

[tomaldinho1]

Ok, well that much I get. But when you said


This is about finishing is not?

As in, using additional details on understat, you could use xG alongside them to really delve into the detail of who could be a good finisher. On its own though it wouldn’t necessarily mean one player was a better finisher than the other without the added context.

 

[quadrant]

As in, using additional details on understat, you could use xG alongside them to really delve into the detail of who could be a good finisher. On its own though it wouldn’t necessarily mean one player was a better finisher than the other without the added context.

xG is not about finishing, nor does it even strongly correlate with finishing, so you can't use xG in a conversation about how good a finisher someone is. You certainly can talk about the role of a striker in creating chances, making good runs etc, but finishing is a separate conversation.

 

[tomaldinho1]

xG is not about finishing, nor does it even strongly correlate with finishing, so you can't use xG in a conversation about how good a finisher someone is. You certainly can talk about the role of a striker in creating chances, making good runs etc, but finishing is a separate conversation.

Well the basic idea of how many people look at it, which is why I wrote the original explanation, is that many do simply do that i.e. overperform = good finisher and underperform = bad finisher.

On an individual level I disagree though, as said, when it is used with other stats. I guess this becomes a conversation about what is 'good' finishing because, for me, xG is very revealing of decision making and that is a big part of what constitutes good finishing in my opinion.

 

[Bastian]

I think this season ETH had already greatly improved our defense. Remember last season at one point we were averaging 20 shots against us. We ended the season at 17.6 shots against us which was 2nd most in the league to Sheffield United with 17.8. So we were right there as the worst in the league at stopping the opposition shooting.

This season iirc it was down a few, lets say 13-14 and today its 11.1 which is 5th in the league after Arsenal, Liverpool, City and Chelsea

ETH's problem was similar to Amorim's problem. Our attacking players couldnt create lots of clear chances and the clear chances we hdid have our players were finishing poorly. In between we had Ruud, and for his games we were finishing better. Then Amorim came and its been the same problem.

We have the joint 9th amount of shots in the league but 11th most shots on target. So we're poor at getting those shots on target let alone beating a goalkeeper

Yes, I did notice that. But our inexcusable profligacy apart, I also didn't really see serious cohesive development from the collective in the first 2-3 months of the season. Maybe the players had already checked out.

We're more defensively solid now, and have thankfully sorted out our set piece defending somewhat (there was a short period where it was worse than anything I can remember by any team, ever), but once this attack is sorted out and we have more than one threatening player (sometimes none), and more pace and power, there'll be less pressure on the collective defensively because teams will be more cautious, whereas now it seems absolutely no one is afraid of us (and up until recently I'd say rightly so).