Ole and xG

OnlyTwoDaSilvas

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So, what's the deal then? Have we scored 10 pure bangers out of nowhere that have fluked their way in? Surely the only way a goal wouldn't count as an expected goal is if it goes right through a flapping goalkeeper, or is a calamitous own goal that the attacking team had little involvement in. If a striker gets a shot on target and it goes in, how could it possibly be an 'unexpected' goal?

It makes a bit more sense the other way. I.e. a goalkeeper making miraculous saves of what looked like a certain goal, of which De Gea frequently does, so that is fairly clear. There was about 4 of those alone vs Spurs.

But which are these goals that United have scored that aren't part of the "xG' total? I'd be interested to see these 10 extra "holy shit how did they score that?!" goals that we've amassed. Whoever is calculating this stat should provide that context, if they don't already.
 

vodrake

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Correct me if I'm wrong, but XG is based on the average likelyhood of scoring an opportunity irrespective of the quality of the player taking the shot? It's saying that we've scored more than the average player would have been expected to score in those situations.

So it's saying that our players are better than the average player? In which case, duh?

Same for the goals conceded. We've conceded less than the expected average goalkeeper would have conceded, because we have a much better than average goalkeeper...

People are skewing this to say we've just been lucky, but it seems to me to just be saying that we surprisingly actually have good players?
 

Cait Sith

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Messi's xG is 19 and his actual goals are 25.

It's accurate on batch data, no individual points.
Messi is literally the only player who consistently scores more than he should and it's completely in line with what every Barca fan will tell you.
 

calodo2003

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As a fairy tale as a data scientist crunching numbers which eventually are able to detect cancer and other sicknesses better than a team of top doctors?

Yes, it is happening.
Not much of an equivalence there, but I get your point.

I have also looked at ‘Billy Ball’ & the overuse of metrics in baseball in the same light even when my hometown club uses such tactics to their betterment. Feels a bit Pollyanna & reaching.
 

mav_9me

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There is a huge misunderstanding about Expected Goals.

Name an elite team that is performing well this season (Man City, Liverpool, Dortmund, Barcelona etc etc) and you will see that they are massively out-performing their expected goals numbers. In the table linked, green is better than expected, red is worse. https://understat.com/league/EPL/2018

Likewise, the teams at the bottom of the table will typically have been a bit unlucky, missed good chances to score in some tight games they ended up losing or drawing.

It's not just this season, it is true of most seasons. When Chelsea won the title under Conte, their expected goals for was 61.80, yet in reality they scored 85. Their expected points 75, in reality 93. Spurs finished 2nd. They too massively out-performed their expected numbers. City last season scored 14 more than expected, and got 9 more points than expected.

This may comes as a huge shock to you but elite players when performing well tend to finish chances at a better rate than an average player would. Elite keepers save shots that many other keepers wouldn't.

If you go through the individual games, Expected Goals didn't like the performances against Spurs and Leicester, matches in which United scored in the first half then sat deep and defended for the rest of the match. In contrast, the Burnley game in which we were 0-2 down, looks like it should have been an easy win for United as we created several big chances to score.

Based purely on chances, the Fulham match could have been a draw, yet anyone watching will have noticed that Fulham had several opportunities in the first 10 mins then almost nothing until the score was 0-3. Ryan Babbel's big chance after 76 mins when he hit the post from close range, was worth 0.59 xG (on average, out of 100 shots from that position, you'd score 59 times). Yet even if he had scored, Fulham would still have struggled to get a draw in the time remaining.

Thanks for the table. On that we have 58 goals for xG of 53 and GA of 38 for xGA of 40.45. Doesn't appear to be that much of a discrepancy does it?
 

Raees

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But that's not the question here. Much of the xG proponents are saying that it will undoubtedly regress back to the bad old days because of the numbers, but ignoring the context, which is where I have my issues with them.

A lot of them are assuming that a) the way we play won't change after Ole has an extended period of time with the players to work on tactical/structural/philosophical preparation (say, during a preseason) - look at what we managed to achieve with just a few days in Dubai, as an example; b) we won't bring in players who will fill the various holes in the squad during the summer; and c) that the players that have been in the team for the last month or so, are the first choice starting players; instead of actually looking at the context of the injuries we faced, and the strength of quality of the opposition.

A fairer comparison for the xG proponents would have been to compare the xG numbers of the likes of City, Utd, Chelsea, Liverpool, Arsenal, Spurs et al against each other during the period of time Ole has been in charge. I'd hazard a guess that their average xG numbers would not have been much different to ours on that basis. It certainly would paint a clearer picture rather than just looking at the last 17 games which Ole has been in charge of which has included a horror run of FA Cup fixtures in addition to difficult league games (whereas of the rest of the top 6, the only team who you could argue have had it as tough, have been Chelsea, and even that would be tenuous).

For instance, if you compared the xG plotmaps for City's (loss), Liverpool's (draw) and Utd's (win) games vs Leicester recently, you'd barely see any difference outside of a .1 or .2 here and there. The fact we were able to grind out a win in testing circumstances such as that is a testament to us, not something to deride Ole or the club.
Yeah I get that argument but XG is a reactive stat in that it tells you what has happened before. It can be used as a predictor of some sort I guess but the best way to use it is analyse past performance and say well we did kind of wing it to some degree but it doesn’t 100% confirm we will get back down to earth because we could easily in the next game start creating chances galore and playing teams off the park.

XG also doesn’t reflect the mental qualities of teams - some teams are great at carving up defences and creating chances but essentially bottle it under pressure - United under Ole have demonstrated nerves of steel which is in of itself an admirable and essential quality.

To call it a useless stat altogether is silly as I do think it’s one of the better ones to come up in recent years.
 

U99ted

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How can one even say it's a pointless statistic when in fact it is SO accurate. Just by sheer statistics alone it predicts Man City to have 73 goals for, 21 against and 69 points. In reality they have 76, 20, 71. It's the most insanely accurate statistic in football that I know of and has nothing to do with "70 % possession means nothing".

Even without statistics it should be clear that this United side isn't going to keep the current win rate alive and it will normalize again. This United team isn't a "14 wins out of 17 games" side.
Go by xG and how “accurate” it is and we don’t even beat Fulham. When we clearly swatted them aside.
 

Dion

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Messi is literally the only player who consistently scores more than he should and it's completely in line with what every Barca fan will tell you.
No actually. Mo Salah had for the last 4 seasons before this one, Leroy Sane has for 4 out of the last 5 seasons, so has Lacazette, Kane does it every year, Song has done it every year but his first at Spurs, Eden Hazard has done it for the last 5 years, Suarez did it for 5 years straight before age caught up with him, Antoine Griezmann has done it 5 years in a row, Nabil Fekir has done it 5 years in a row, Dybala has done it 4 years in a row, Icardi did it 4 years in a row, Ciro Immobile has done it 3 years in a row at Lazio, Higuain did it 4 years in a row. And those are just stats from players who did it in the last 5 years.

Messi has scored 165 league goals in the last 5 seasons with an xG of 137. Kane has 120 with an xG of 101. That's almost the exact same level of over-performance over the same time period. Eden Hazard has over-performed even more than both.
 
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Rish Sawhney

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Messi is literally the only player who consistently scores more than he should and it's completely in line with what every Barca fan will tell you.
Well Barca should fire him then. Clearly it can't last.

EDIT: Also, since it looks like Liverpool and City are also overperforming their xStats does that mean their form can't last either?
 

FlawlessThaw

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No actually. Mo Salah had for the last 4 seasons before this one, Leroy Sane has for 4 out of the last 5 seasons, so has Lacazette, Kane does it every year, Song has done it every year but his first at Spurs, Eden Hazard has done it for the last 5 years, Suarez did it for 5 years straight before age caught up with him, Antoine Griezmann has done it 5 years in a row, Nabil Fekir has done it 5 years in a row, Dybala has done it 4 years in a row, Icardi did it 4 years in a row, Ciro Immobile has done it 3 years in a row at Lazio, Higuain did it 4 years in a row. And those are just stats from players who did it in the last 5 years.
Seems like the top players as well as the top clubs in the PL outperform xG. Funny that.
 

Cheesy

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A good point I saw on Twitter.

True. If he'd, say, lost two more games then he has, and if he'd drawn a couple more, then we'd likely still be happy. And in many ways last night, if anything, almost makes his run even better in that the one game he's lost was in a two-legged tie we eventually emerged from successfully anyway.
 

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I think right now it's just too small of a sample size. We have outliers like our PSG smash and grab skewing the numbers too much. I think xG is very valuable but it definitely needs more context here (the fixtures we went through incl. Pool, Chelsea, Arsenal, PSG 2x are expected to be tight cagy affairs where we don't cut these teams open as we want). We've also had the 5-1 after Mou left where the xG for us was definitely not 5.

So far, the football passes the eye test, the whole squad is behind the manager and morale is high. These things can't be quantified but they're probably the most important things a manager can do for the squad and that by itself deserves a permanent contract.
 

Anustart89

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So, what's the deal then? Have we scored 10 pure bangers out of nowhere that have fluked their way in? Surely the only way a goal wouldn't count as an expected goal is if it goes right through a flapping goalkeeper, or is a calamitous own goal that the attacking team had little involvement in. If a striker gets a shot on target and it goes in, how could it possibly be an 'unexpected' goal?

It makes a bit more sense the other way. I.e. a goalkeeper making miraculous saves of what looked like a certain goal, of which De Gea frequently does, so that is fairly clear. There was about 4 of those alone vs Spurs.

But which are these goals that United have scored that aren't part of the "xG' total? I'd be interested to see these 10 extra "holy shit how did they score that?!" goals that we've amassed. Whoever is calculating this stat should provide that context, if they don't already.
If you take a hundred shots from the edge of the box and a little bit to the left you'll maybe see that 10 times out of 100 it goes into the net. That makes the next shot from that position in similar circumstances have an xG of 0.10, ie 0.10 goals expected from every shot in that situation, or one goal scored per ten shots from that position.

What that means is that if a team takes ten of those shots in a game (and creates no other chances) and score two goals, they will have amassed a total xG of 1.0 (0.10x10) while having an actual goals scored value of 2. In that situation, one interpretation is that the players are over-performing and would given enough time regress back to the mean (ie score one goal instead of two), while some others say that it's fairly natural that a team with above average players will outperform the average number.

What this essentially means for us is that we've scored more goals than we would have been expected to based on the amount and quality of chances we've created. If we had scored fewer goals than our xG value, then it would have meant that we'd missed a lot of good goalscoring opportunities (but depending on how big the xG number is, it would have been an indication of how many chances we create as well).
 

Dion

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If you take a hundred shots from the edge of the box and a little bit to the left you'll maybe see that 10 times out of 100 it goes into the net. That makes the next shot from that position in similar circumstances have an xG of 0.10, ie 0.10 goals expected from every shot in that situation, or one goal scored per ten shots from that position.

What that means is that if a team takes ten of those shots in a game (and creates no other chances) and score two goals, they will have amassed a total xG of 1.0 (0.10x10) while having an actual goals scored value of 2. In that situation, one interpretation is that the players are over-performing and would given enough time regress back to the mean (ie score one goal instead of two), while some others say that it's fairly natural that a team with above average players will outperform the average number.

What this essentially means for us is that we've scored more goals than we would have been expected to based on the amount and quality of chances we've created. If we had scored fewer goals than our xG value, then it would have meant that we'd missed a lot of good goalscoring opportunities (but depending on how big the xG number is, it would have been an indication of how many chances we create as well).
The important clarification here is the "you" is every shot that Opta has measured being taken from that spot. That means every Ronaldo pot-shot, every Jonjo Shelvey swipe etc. not just every time Messi does it.
 

Dion

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Well Barca should fire him then. Clearly it can't last.

EDIT: Also, since it looks like Liverpool and City are also overperforming their xStats does that mean their form can't last either?
Spurs should clearly sell Kane and Chelsea should ditch Hazard. They were really lucky they consistently outperformed their xG by so much for half a decade.
 

NoPace

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I think it shows that we don't create enough chances and we give up too many because we don't control games.

But that's less on Ole and more on us only having 2 world class players in Pogba and De Gea and then Shaw, Lindelof and Herrera are up to the standard. The forwards are still young (Rash, Martial) and inconsistent (Lukaku) but we should back them, but we need 4 starters rather than having an aging Matic, technically poor Smalling, Ashley Young at RB and Lingard/Mata whoever you want to call our RW.

Plug those last 4 players into City's team. What's their XG?

Sane-Aguero-Lingard
--DeBruyne-Silva----
--------Matic---------
Young-----------Walker
--Otamendi-Smalling-
-------Ederson--------

and suddenly the defense looks shaky on the ball, Matic has way too much room to cover and while Lingard's composed finishing means his numbers aren't awful, he can't beat a man out wide and is blunting City's attack's on that wing.
 

Tarrou

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To be honest we have rode our luck a little bit under Ole.

We have still performed brilliantly, but there are two/three results that could've easily gone the other way.
 

Anustart89

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The important clarification here is the "you" is every shot that Opta has measured being taken from that spot. That means every Ronaldo pot-shot, every Jonjo Shelvey swipe etc. not just every time Messi does it.
Exactly, so in my world any above average team should be outperforming their xG, which means that doing precisely that shouldn't be used as a criticism of a team, but rather the criticism should be directed at a good team failing to outperform xG for/against.
 

harms

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Messi's xG is 19 and his actual goals are 25.

It's accurate on batch data, no individual points.
Messi is one of the very few people who completely shits on xG stat throughout many seasons. It's not surprising as his game is beyond any rational explanation.

Aguero is a great example of how xG work though. I'm sure that all of us can agree that he is a brilliant finisher, but his most important quality is not actually kicking the ball into the net, but getting into the most dangerous positions consistently. A difference between a good and a bad finisher is that, quite often, a good one will be better positioned before actually taking a shot.

Despite scoring 40 goals over the 2016/17 and 2017/18 seasons (excluding free kicks), Aguero has an estimated outperformance of almost exactly 1, his 218 shots adding up to an xG total of 40.8. He's also somewhat one-footed, with his left-footed goals substantially trailing the xG tally of his left-footed shots. Expected goals data on understat.com indicates that, over the last 5 seasons, Aguero has scored 95 goals from an xG tally of 90.3, implying an outperformance of 1.05
Ronaldo is an even better example. His shots to goal ratio was questioned for years before the xG was even invented, but no other player can get into the goalscoring positions as often as he does (not even Messi). And no one would say that he is a lousy finisher, or even an average one.
 

bosnian_red

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To be honest we have rode our luck a little bit under Ole.

We have still performed brilliantly, but there are two/three results that could've easily gone the other way.
As you would expect when you play PSG/Spurs/chelsea/arsenal/leicester/palace all away and then PSG/Liverpool at home. Not to mention the injuries. Weve done terrific whatever way you look at it.
 

Dion

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Messi is one of the very few people who completely shits on xG stat throughout many seasons. It's not surprising as his game is beyond any rational explanation.

Aguero is a great example of how xG work though. I'm sure that all of us can agree that he is a brilliant finisher, but his most important quality is not actually kicking the ball into the net, but getting into the most dangerous positions consistently. A difference between a good and a bad finisher is that, quite often, a good one will be better positioned before actually taking a shot.
I see you haven't read my other post yet. I would be interested to hear your thoughts on it.

No actually. Mo Salah had for the last 4 seasons before this one, Leroy Sane has for 4 out of the last 5 seasons, so has Lacazette, Kane does it every year, Song has done it every year but his first at Spurs, Eden Hazard has done it for the last 5 years, Suarez did it for 5 years straight before age caught up with him, Antoine Griezmann has done it 5 years in a row, Nabil Fekir has done it 5 years in a row, Dybala has done it 4 years in a row, Icardi did it 4 years in a row, Ciro Immobile has done it 3 years in a row at Lazio, Higuain did it 4 years in a row. And those are just stats from players who did it in the last 5 years.

Messi has scored 165 league goals in the last 5 seasons with an xG of 137. Kane has 120 with an xG of 101. That's almost the exact same level of over-performance over the same time period. Eden Hazard has over-performed even more than both.
 

adexkola

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When I flip a coin 5 times and get tails 5 times doesn't make the probability of getting tails 100 %. It should be clear what I mean. United is overperforming.

Do you think United will keep this rate up over a prolonged period of time (let's say 70 games)?
What if you're a Bayesian though?
 

Rish Sawhney

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So according to this table, the top 4 looks as follows:

No Team M W D L G GA PTS xG xGA xPTS
1 Manchester City 29 23 2 4 76 20 71 72.84-3.16 21.25+1.25 68.94-2.06
2 Liverpool 29 21 7 1 64 15 70 59.07-4.93 21.91+6.91 63.56-6.44
3 Tottenham 29 20 1 8 56 30 61 48.36-7.64 36.70+6.70 48.35-12.65
4 Manchester United 29 17 7 5 58 38 58 53.19-4.81 40.45+2.45 47.29-10.71

What does this say about Liverpool (who have xPTS of 63.56 but have 70 points) and Spurs (who're overperforming even more than we are)?

Messi is one of the very few people who completely shits on xG stat throughout many seasons. It's not surprising as his game is beyond any rational explanation.

Aguero is a great example of how xG work though. I'm sure that all of us can agree that he is a brilliant finisher, but his most important quality is not actually kicking the ball into the net, but getting into the most dangerous positions consistently. A difference between a good and a bad finisher is that, quite often, a good one will be better positioned before actually taking a shot.
Yeah if you ignore all the other people that overperform their xG.

See:
No actually. Mo Salah had for the last 4 seasons before this one, Leroy Sane has for 4 out of the last 5 seasons, so has Lacazette, Kane does it every year, Song has done it every year but his first at Spurs, Eden Hazard has done it for the last 5 years, Suarez did it for 5 years straight before age caught up with him, Antoine Griezmann has done it 5 years in a row, Nabil Fekir has done it 5 years in a row, Dybala has done it 4 years in a row, Icardi did it 4 years in a row, Ciro Immobile has done it 3 years in a row at Lazio, Higuain did it 4 years in a row. And those are just stats from players who did it in the last 5 years.

Messi has scored 165 league goals in the last 5 seasons with an xG of 137. Kane has 120 with an xG of 101. That's almost the exact same level of over-performance over the same time period. Eden Hazard has over-performed even more than both.
 

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I think that's interesting and wouldn't discount it as nonsense. The record after Ole took over is just insanly strong and I don't think maintaining a 100 point pace is realistic and expected, so it has some merit. However even if we see some slight drop in the goals scored and conceded it's good enough to contend for trophies. Doing a fantastic job regardless and a massive improvement from Jose in all aspects.
 

jem

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Stat for people who prefer talking about football instead of actually watching and enjoying it.
I agree - it's even worse with baseball. I think it's also just a lot of people making up stuff to try make themselves appear relevant. All you need to do is watch United now, and compare it with the Mourinho era and the difference in quality is there for all to see (but that's the thing: you actually have to watch in order to see it.)
 

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To be honest we have rode our luck a little bit under Ole.

We have still performed brilliantly, but there are two/three results that could've easily gone the other way.
It goes for our non-wins as well. We could have scored against Liverpool and were unlucky with injuries, we should have probably beaten Burnley.
 

Anustart89

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No actually. Mo Salah had for the last 4 seasons before this one, Leroy Sane has for 4 out of the last 5 seasons, so has Lacazette, Kane does it every year, Song has done it every year but his first at Spurs, Eden Hazard has done it for the last 5 years, Suarez did it for 5 years straight before age caught up with him, Antoine Griezmann has done it 5 years in a row, Nabil Fekir has done it 5 years in a row, Dybala has done it 4 years in a row, Icardi did it 4 years in a row, Ciro Immobile has done it 3 years in a row at Lazio, Higuain did it 4 years in a row. And those are just stats from players who did it in the last 5 years.

Messi has scored 165 league goals in the last 5 seasons with an xG of 137. Kane has 120 with an xG of 101. That's almost the exact same level of over-performance over the same time period. Eden Hazard has over-performed even more than both.
This paints a cracking picture, since you can see that players who are widely regarded as the best around are consistently over-performing their xG. To then draw the opposite conclusion with regards to teams, ie that xG over-performance from a team is bad, which people tend to be doing with the regression to the means argument, is beyond ricidulous.

What you want to be doing, as a team, is to amass a set of players who can rack up high numbers in the xG department, but still outperform it. If you've got a high xG but are under-performing in terms of goals scored, then your finishing isn't good enough. Now that might win you a league anyway if you're creating so many chances that you'll outscore the opponent anyway, but by buying better players you're not necessarily changing the outperformance ratio, but you're pushing the actual goals scored and xG up to higher levels.
 

bosnian_red

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So, what's the deal then? Have we scored 10 pure bangers out of nowhere that have fluked their way in? Surely the only way a goal wouldn't count as an expected goal is if it goes right through a flapping goalkeeper, or is a calamitous own goal that the attacking team had little involvement in. If a striker gets a shot on target and it goes in, how could it possibly be an 'unexpected' goal?

It makes a bit more sense the other way. I.e. a goalkeeper making miraculous saves of what looked like a certain goal, of which De Gea frequently does, so that is fairly clear. There was about 4 of those alone vs Spurs.

But which are these goals that United have scored that aren't part of the "xG' total? I'd be interested to see these 10 extra "holy shit how did they score that?!" goals that we've amassed. Whoever is calculating this stat should provide that context, if they don't already.
They dont include penalties into the total, they separate I'm pretty sure. So really its like 36ish expected goals compared to 39 actual. (Big deal right).
 

Dave89

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Speaking as an auditor, it's not a statistic, it's an estimate. Estimates can say whatever you want them to say.
 

harms

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I see you haven't read my other post yet. I would be interested to hear your thoughts on it.
This is a good article on the matter, better than anything that I can come up with on my own:
https://www.optasportspro.com/news-analysis/on-the-topic-of-expected-goals-and-the-repeatability-of-finishing-skill/

Why the positioning (and the xG score) is more important than the G/xG ratio. Despite the fact that better forwards will score more consistently than worse ones, obviously.
 

Dion

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This is a good article on the matter, better than anything that I can come up with on my own:
https://www.optasportspro.com/news-analysis/on-the-topic-of-expected-goals-and-the-repeatability-of-finishing-skill/

Why the positioning (and the xG score) is more important than the G/xG ratio. Despite the fact that better forwards will score more consistently than worse ones, obviously.
None of that really addresses the issue that Messi is far from the only player who consistently outperforms his xG. It's actually very common among forwards at top clubs.
 

Dave89

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Apologies if I've missed this, but we should do a quick sense check.

Does the sum of say every premier league player's actual goals less expected goals equal close to zero? If the xg goals figure truly was expected, then over such a large sample size (200 starting outfield players per gameweek, plus say 50 subs, over 38 game weeks = 9500 data points), then the total goals actually scored in the league should be very close to the expected goals.

If it's not, it's a shit metric by its own definition.
 

kundalini

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Apologies if I've missed this, but we should do a quick sense check.

Does the sum of say every premier league player's actual goals less expected goals equal close to zero? If the xg goals figure truly was expected, then over such a large sample size (200 starting outfield players per gameweek, plus say 50 subs, over 38 game weeks = 9500 data points), then the total goals actually scored in the league should be very close to the expected goals.

If it's not, it's a shit metric by its own definition.
I believe most of the models have used the data from last 3+ years for the top European leagues, PL, La Liga, Bundesliga, Serie A and Ligue 1 to come up with their figures. Over the course of that period of time (3 to 5 years) the number of goals scored equals the expected goals total. In any one season, the real goals scored total may be slightly higher, or slightly lower than the expected figure.
 

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I agree - it's even worse with baseball. I think it's also just a lot of people making up stuff to try make themselves appear relevant. All you need to do is watch United now, and compare it with the Mourinho era and the difference in quality is there for all to see (but that's the thing: you actually have to watch in order to see it.)
We have better xG stats under Ole than under Mourinho. However our run of points is better than City's last year, while only an idiot will claim that we are playing better than City last year.

xG actually agrees with what we see in the pitch, but disagrees with the table (we aren't ever going to get 102 points in a season playing like this, which is what Solskjaertable says).
 

Dave89

Full Member
Joined
Nov 30, 2007
Messages
17,553
I believe most of the models have used the data from last 3+ years for the top European leagues, PL, La Liga, Bundesliga, Serie A and Ligue 1 to come up with their figures. Over the course of that period of time (3 to 5 years) the number of goals scored equals the expected goals total.
If I understand that correctly, they've confirmed that, working backwards, the models fit the source data used (which you would expect), but for the first full season of new predictions, did it fit?
 

Revan

Assumptionman
Joined
Dec 19, 2011
Messages
38,672
Location
CA
Speaking as an auditor, it's not a statistic, it's an estimate. Estimates can say whatever you want them to say.
Can you please help me then to publish the next paper? I am desperately in need for better results than other competing models.