Why xG is Irrelevant Nonsense

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Dr Rocktopus

Dr Rocktopus

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I hate xG almost as much as VAR. It's subjective bullshit that completely fails to grasp the fact that football (and life in general, for that matter) isn't something that can be broken down into black and white, yes/no binary outcomes.

The ball is passed to a player in an open position with a clear sight of goal. He misses. Does xG take into account any of the following:

The player may have ran the length of the pitch to be in that position, and is physically exhausted.

When the ball arrives it is spinning in a way that makes it less likely to hit the target.

The condition of the pitch.

The condition of the wind.

The condition of their boots.

I'm purposely being a bit ridiculous, but the point is that there are so many variables that can affect what constitutes a chance. None of this even factors in the positive things that happen for the player to create that chance in the first place.

It might look good on paper, but xG is meaningless.
 
Like almost every stat, it’s not pointless, but there’s very little point.

Pass completion? Tapping four yard passes to your mate are counted. Wow.

Possession? So? Doesn’t matter if you do nothing with it.

Goals scored and goals conceded are all that really matter.
 
Shots off/on target is the other one that bothers me, or at least the implication that on target is always the better attempt.

Bale's screamer that beat the goalkeeper but hit the crossbar: Off target

Lamela rolls the ball at 2mph into the goalkeeper's arms: On target.
 
I hate xG and the hyper fixation on it. I am sure that it is a useable stat for people that actually work in football statistics. But we fans should stay far away from discussing the game based off of it because it is a incomplete model that most fans do not really understand to begin with.

It has also helped usher in a hyper fixation on measuring football through numbers instead of also calculating in other factors, both on and off pitch. More and more clubs are scouting almost exclusively by numbers now and not looking at if the player will slot into the system run by their manager or not.

If you want to scout like that you need to have a very detailed formula to run the numbers by so that you get the best possible players for your managers system.
 
I think I've made myself pretty clear about what I think of all this nonsense in previous posts. And don't get me started on players' ratings on computer games .....................:harryhmm:
 
I'm not a huge fan of using stats in football, but I do realise some have their place. In my opinion xG is one that should be consigned to the bin though.
Dr Rocktopus Dr Rocktopus covers it pretty well in the opening post, but the other point for me is that in football nothing should be expected. One of the things that makes football the beautiful game is that anything can happen so expecting certain things, in this case goals, is silly. There are so many different little things that can prevent a goal and the stat doesn't take that into account.
 
Mandy said:
I'm not a huge fan of using stats in football, but I do realise some have their place. In my opinion xG is one that should be consigned to the bin though.
Dr Rocktopus Dr Rocktopus covers it pretty well in the opening post, but the other point for me is that in football nothing should be expected. One of the things that makes football the beautiful game is that anything can happen so expecting certain things, in this case goals, is silly. There are so many different little things that can prevent a goal and the stat doesn't take that into account.
Click to expand...

Unexpected beach ball!
 
Teoff Gate said:
Don't need stats to show how shit we are
Click to expand...

I agree, but xG is good looking back in the past to illustrate to people when we were good or when we were shit. For example some people airbrush how bad we were for the last 18 months under Poch but when you look at expected goals scored before and conceded before that period, then during it, then when Mourinho took over, you can see when it started to go tits up. It is on this link after the first paragraph:

statsbomb.com

Tottenham Hotspur: Season Preview 2020-21 - StatsBomb | Data Champions

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statsbomb.com statsbomb.com

But as something going forward and for predicting things I’m not so certain.
 
GDP per capita is a useless statistic because there are poor people who make 10k pa and rich people who make 500k pa!!

Generalizations aren't useless because they don't explain every single factor. It's the entire point of them.

Almost every team and players perform similar to their xG or xP over the course of a season.

If xG was useless nonsense, why was it proven right when it suggested we were wildly outperforming to an unsustainable degree when we scored 3 goals from 4 shots early in the season?

Of course weather and pitch conditions have an impact on the chance of scoring from a shot. But the averages obviously take that into considerations.

Deviations from the mean doesn't mean the mean isn't a reasonable measurement to use as a baseline.
 
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