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The xG nonsense

Definitely Maybe said:
Again though, if we're outperforming our xG it suggests our attacking players are more clinical than average. Which you go on to agree with but then criticise as nonsense?

You keep referencing Kane who is arguably the best striker in the world. Is he the most clinical striker in the world? The answer is no, his goal conversion rate is 22% this season which puts him 35th out of all players in the top 5 European leagues. Will Osula is 3rd at 30%. Kane's conversion rate on previous seasons usually ranges from 17% to 20%, this was the best season of his career.

Is Osula a better goalscorer than Kane? Absolutely not, but what sets them apart isn't the fact Kane is a better finisher, its because Kane's movement and intelligence is on another planet and he consistently gets into great positions where he can get shots away from dangerous areas. There's loads of research which shows the best strikers aren't the ones with the highest conversion rates and the ideas of the best strikers being the best finishers is a bit of a myth, the reality is the best strikers are the ones with the highest xG because they get into better positions than anyone else.

If you think of Sunderland as an example, we've had loads of shit strikers but the only one I can remember who actually missed loads of chances was Altidore. The likes of Grigg and Graham weren't shit because they kept missing chances, they were shit because they were miles off the pace and never got a sniff of anything near the goal.

You also keep mentioning Leeds underperforming xG - who is their main striker? Calvert-Lewin, who historically has always underperformed xG and has had spells this season and throughout his career where everything he touched went in followed by long goal droughts. Leeds and DCL's xG data suggests they're a fairly creative team who aren't great at putting away those chances. Ours suggests we aren't particularly great at creating chances but good at finishing what we do create. There's no positive or negative to either of those beyond that, just an observation. Statistically, teams generally do revert to the mean over the long term but anyone telling you a team should have finished here or there because of xG is talking shit and missed the point of it.

There's a couple of examples that are frequently quoted - in Klopp's final season at Dortmund they had a terrible first half of the season and came in for a lot of criticism, but Klopp pointed out their xG data was almost identical to the season they won the league, they'd just been unlucky and their luck would turn around. He was laughed at but sure enough they had a great second half of the season without doing anything differently. And in our League One season under Jack Ross there was holy hell on on here when pundits suggested we weren't as good as results suggested because we'd been lucky with the likes of McGeady and Maguire scoring screamers and McLaughlin saving everything despite us giving away loads of chances. That George Elek received a load of abuse for predicting Barnsley to go to ahead of us, especially after we beat them 4-2. Sure enough though the screamers stopped going in, we started to concede more and slipped away. Both are examples of teams under or over performing xG and eventually reverting to the mean.
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Stopped reading at keep mentioning Kane. Mentioned him once
 

Kent Boy 2 said:
Perfect description. Fortunately the majority of football clubs (including ours) have people who are in the middle.

What about in the other 52% of games?
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It was significant, as I'v said but overall it's about 52%, not enough to base a league table upon. Other factors are deciding tight games which Xg doesn't show.
If you're going to use it to predict results it would have to have some chance significance built into it, a pen goes down as 0.7 even if its the last minute of a 3-1 defeat, in Xg terms that might mean the predicted result goes the other way, which is a bit silly.
 
I think some people just hear "expected goals" and think "What? Expected? Nah mate, you either score or you don't. Whatta loada rubbish"

It's about measuring the frequency and quality of chance creation.

A good example of how everyone can use it to gain a better understanding of an individual game:

Sunderland play Newcastle at the weekend, but you can't make it as you're at a funeral or something.

Later that day, you pull out your phone and fire up your footballing score app of choice to check the result...

"Sunderland 1 Newcastle 1"

Ok, so it was a draw, but you want to get a better understanding of how the game went, so you check out the statistics.

(for the sake of argument)

Possession is bang on 50/50

Both teams had 10 shots

Both teams had 5 on target

That means the game was fairly even then right?

XG has Sunderland as 0.5XG but Newcastle are at 3.25XG

That shows that Newcastle had by far the better chances and that Sunderland were lucky to get a point.


It is as useful a metric as any when used correctly
 
Charmless Man said:
Did he say that?

Intriguing if he did because the way City played very much suggested he did have time for it. So many of their goals were cut backs into the six yard box which would always produce a decent xG score on the chance.
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A lad who worked at city was on SSN yesterday discussing it, said Pep wouldn’t entertain the notion that xg was a thing.
 
johnkaysleftleg said:
It was significant, as I'v said but overall it's about 52%, not enough to base a league table upon. Other factors are deciding tight games which Xg doesn't show.
If you're going to use it to predict results it would have to have some chance significance built into it, a pen goes down as 0.7 even if its the last minute of a 3-1 defeat, in Xg terms that might mean the predicted result goes the other way, which is a bit silly.
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In how many games this season was a penalty given in the last minute of a 3-1 defeat in the PL? And in how many of those games did it alter the xG result? A fraction of a percent - at best? So it’s basically a pointless example.

xG is consistent with the final score in matches ~60% of the time. Those people who treat it as gospel don’t understand it. Those people who totally deride it, also don’t understand it. Fortunately there are people who both understand it and know how to use it.
 
SuperKevsLeftBoot said:
To completely prove a point how bllx it is.

Brobbeys chance against Chelsea was a 0.33 which is outrageous.

He shoots from 8/9 yards out at a perfect angle and fluffs is completely. Vast majority of the strikers … way more than a 3rd would have scored that.

It was a terrible miss which didn’t cost us but the goal is so open and at the near post. Wilson would score that 99 times out of 100.

How on earth is that a 0.33. Pure made up bllx.

This has happened numerous times throughout the season. Which is why it’s probably made our “xg” worse than it is.

Someone should screenshot it just as he shoots. It’s a shocking miss.
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Apart from the fact he’s at a small angle from the side of the box, with a defender wrestling with him?
 
DJ Doubt said:
I think some people just hear "expected goals" and think "What? Expected? Nah mate, you either score or you don't. Whatta loada rubbish"

It's about measuring the frequency and quality of chance creation.

A good example of how everyone can use it to gain a better understanding of an individual game:

Sunderland play Newcastle at the weekend, but you can't make it as you're at a funeral or something.

Later that day, you pull out your phone and fire up your footballing score app of choice to check the result...

"Sunderland 1 Newcastle 1"

Ok, so it was a draw, but you want to get a better understanding of how the game went, so you check out the statistics.

(for the sake of argument)

Possession is bang on 50/50

Both teams had 10 shots

Both teams had 5 on target

That means the game was fairly even then right?

XG has Sunderland as 0.5XG but Newcastle are at 3.25XG

That shows that Newcastle had by far the better chances and that Sunderland were lucky to get a point.


It is as useful a metric as any when used correctly
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Yep.

Or to use another example, when Steve Bruce was West Brom manager they were bottom of the Championship and couldn't win a game but their xG was always quite a bit higher than the opposition every game.

Did that make them unlucky? Possibly. But if you delved a bit deeper you'd see they created nothing but tended to concede early in games, the opposition would go 2-0 up then they'd throw everything forward late in the game while the opposition sat back.

Bruce was sacked and Carlos Coberan came in who was much more disciplined and they shot up the table and just missed out on the play offs.

Main takeaway is that they were never a bad team and perfectly capable of creating chances but Bruce couldn't organise or motivate them for shit. Once a better manager came in and sorted their defence out and got them to focus for 90 minutes they turned it around, just missed out that year but finished top 6 the following season.

If you only looked at the league table you'd think they were the worst team in the league. If you delved a bit deeper into the data you'd see they weren't.
 
At the end of the day xG is just another stat. It’s a very high level one too, like possession for example.

It indicates things but doesn’t show the full picture

The problem with xG is everyone continues to use it like it’s the deciding stat, it’s not. xG is just a stat from thousands of similar chances and the outcome from them, it’s maths, not an opinion.

The xG table got 80% of teams spot on this season, only 4 teams were wrong by 5 or more spots.

Us, who relied on blocking shots, sitting deep and being clinical with minimal chances. xG is cumulative so when we sit in and face a lot of shots it’s going to go up. Then as I say we relied on taking our chances, so xG is lower.

Villa, who went on a big run of scoring more goals from outside the box then in it.

The others were Chelsea and palace, who severely struggled to take the chances they made.

According to understat our xG was ~43. We scored 42, which backs up the clinical aspect. Our xGA was ~60 and we conceded 48. Which backs up the fact we sit deep allow and block shots, all of our defenders are within the top 10/15/20% of defenders for blocked shots.

To remember aswell xG is the measure of the CHANCE, not the finish. So that’s if you shoot from the position the shot is taken, taking into account where defenders are, where the goalkeeper is, whether it’s came from a cross, a dribble, what type of shot (volley, header) how many times has chances like that been scored. If the player then miss kicks the ball, it’s still the same xG chance.

How many games this season have we won by fine margins, because we defended with resilience and took our minimal chances. Those can go the other way.

Game state had to be taken into account to. We could go 1-0 up early, sit back and create nothing else for the rest of the game. Or we could go 1-0 down early then have 30 shots trying to get back in the game and create high cumulative xG. It’s just another reason why xG can’t just be face value.

xG is maths, it’s a probability. The probability says it expects to lose more than we win this season, but there is also a probability we don’t. Let’s say something has a 1 in 20 chance of happening, that means it can still happen.

Next season we will sign players, we will likely improve our playstyle and therefore next seasons xG table may look different.

But xG has shown long term to be useful.
 
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Kent Boy 2 said:
In how many games this season was a penalty given in the last minute of a 3-1 defeat in the PL? And in how many of those games did it alter the xG result? A fraction of a percent - at best? So it’s basically a pointless example.

xG is consistent with the final score in matches ~60% of the time. Those people who treat it as gospel don’t understand it. Those people who totally deride it, also don’t understand it. Fortunately there are people who both understand it and know how to use it.
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This is how I use it:
People use xG to take shots at Sunderland and how low their xG is... then we end up finishing 7th and in Europe... then I start a thread calling it nonsense and laugh at all the xG experts (nerds) who predicted failure... THE END!
 
Kent Boy 2 said:
In how many games this season was a penalty given in the last minute of a 3-1 defeat in the PL? And in how many of those games did it alter the xG result? A fraction of a percent - at best? So it’s basically a pointless example.

xG is consistent with the final score in matches ~60% of the time. Those people who treat it as gospel don’t understand it. Those people who totally deride it, also don’t understand it. Fortunately there are people who both understand it and know how to use it.
Click to expand...

Last season it was just under 52% of the time not 60%.
Consolation goals happen all of the time, as do chances for already beaten teams, they don't effect the result one bit but are included in Xg calculations. If you want to put meaning in Xg tables then fine, having attempted to look into it closely my conclusion is they are a big overreach. The data I've looked at suggests Sunderland have little to worry about as regards being 'relegated' by Xg
 
SuperKevsLeftBoot said:
don’t say the word fact when you’re wrong. You look stupid.
Clearly you’ve not seen the chance.
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Apologies I got the angle wrong, however watch it back, the moment he kicks the shot Fofana is literally pushing him over. That drops the xG to 0.33 over what would be higher with no defenders around.
IMG_2644.jpeg
 

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MadMackem7 said:
At the end of the day xG is just another stat. It’s a very high level one too, like possession for example.

It indicates things but doesn’t show the full picture

The problem with xG is everyone continues to use it like it’s the deciding stat, it’s not. xG is just a stat from thousands of similar chances and the outcome from them, it’s maths, not an opinion.

The xG table got 80% of teams spot on this season, only 4 teams were wrong by 5 or more spots.

Us, who relied on blocking shots, sitting deep and being clinical with minimal chances. xG is cumulative so when we sit in and face a lot of shots it’s going to go up. Then as I say we relied on taking our chances, so xG is lower.

Villa, who went on a big run of scoring more goals from outside the box then in it.

The others were Chelsea and palace, who severely struggled to take the chances they made.

According to understat our xG was ~43. We scored 42, which backs up the clinical aspect. Our xGA was ~60 and we conceded 48. Which backs up the fact we sit deep allow and block shots, all of our defenders are within the top 10/15/20% of defenders for blocked shots.

To remember aswell xG is the measure of the CHANCE, not the finish. So that’s if you shoot from the position the shot is taken, taking into account where defenders are, where the goalkeeper is, whether it’s came from a cross, a dribble, what type of shot (volley, header) how many times has chances like that been scored. If the player then miss kicks the ball, it’s still the same xG chance.

How many games this season have we won by fine margins, because we defended with resilience and took our minimal chances. Those can go the other way.

Game state had to be taken into account to. We could go 1-0 up early, sit back and create nothing else for the rest of the game. Or we could go 1-0 down early then have 30 shots trying to get back in the game and create high cumulative xG. It’s just another reason why xG can’t just be face value.

xG is maths, it’s a probability. The probability says it expects to lose more than we win this season, but there is also a probability we don’t. Let’s say something has a 1 in 20 chance of happening, that means it can still happen.

Next season we will sign players, we will likely improve our playstyle and therefore next seasons xG table may look different.

But xG has shown long term to be useful.
Click to expand...
DJ Doubt said:
I think some people just hear "expected goals" and think "What? Expected? Nah mate, you either score or you don't. Whatta loada rubbish"

It's about measuring the frequency and quality of chance creation.

A good example of how everyone can use it to gain a better understanding of an individual game:

Sunderland play Newcastle at the weekend, but you can't make it as you're at a funeral or something.

Later that day, you pull out your phone and fire up your footballing score app of choice to check the result...

"Sunderland 1 Newcastle 1"

Ok, so it was a draw, but you want to get a better understanding of how the game went, so you check out the statistics.

(for the sake of argument)

Possession is bang on 50/50

Both teams had 10 shots

Both teams had 5 on target

That means the game was fairly even then right?

XG has Sunderland as 0.5XG but Newcastle are at 3.25XG

That shows that Newcastle had by far the better chances and that Sunderland were lucky to get a point.


It is as useful a metric as any when used correctly
Click to expand...


exactly. i've tried to explain this to people a million times but they are too stupid to even consider having a conversation about it. ''xG means fuck all, all that matters is how many goals you score compared to the other team''

of course, that is true.

but corners, possession, shots on target, shots off target, number of passes, number of forward passes, successful tackles, headers won.... all are stats that can be used to build a picture of how a game went or how a player performed. it won't tell you the whole picture, but it will give you some data and evidence to build up a picture

generally speaking, the teams who score the most goals over a season and concede the least, finish higher up. the teams who score less and concede more, finish lower down. its a general trend

yes, you could theoretically win the league with a negative goal difference, but its extremely unlikely
 
A good analysis here, Mukiele’s stats are mind blowing.
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tunstallhill said:
exactly. i've tried to explain this to people a million times but they are too stupid to even consider having a conversation about it. ''xG means fuck all, all that matters is how many goals you score compared to the other team''

of course, that is true.

but corners, possession, shots on target, shots off target, number of passes, number of forward passes, successful tackles, headers won.... all are stats that can be used to build a picture of how a game went or how a player performed. it won't tell you the whole picture, but it will give you some data and evidence to build up a picture

generally speaking, the teams who score the most goals over a season and concede the least, finish higher up. the teams who score less and concede more, finish lower down. its a general trend

yes, you could theoretically win the league with a negative goal difference, but its extremely unlikely
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The fact is xG isn’t subjective it’s a mathematical calculation. That’s what people don’t get
ir35 said:
A good analysis here, Mukiele’s stats are mind blowing.
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Yes saw this earlier, exactly what I was saying about blocked shots despite high xG, hope this helps people understand
 
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