Crunching Numbers: What's The Deal With Players That Outperform Their Expected Goals...

Okay, this article was wayyyy longer than I first thought it would be....

Dec 16, 2020

Disclaimer: I’ve got a small partnership with eBay. If you click a link to eBay, I might earn a small commission on what you buy. It’s tiny and doesn’t cost you anything, but keeps the lights on here and means this newsletter can continue to be free.

Over the weekend I was watching Tottenham play, and as is becoming tradition, I saw Son score…..

I was on Twitter during the game, and saw this tweet from Infogol, which summed up what I kinda already could see. Son’s finishing this year has been awesome.

Infogol @InfogolApp

Son Heung-min has scored 10 goals in the Premier League this season from 3.90 xG. 🎯 That's an overperformance of 156%. Elite finishing. 🔥 #THFC ⚪

It got me thinking a little about expected goals. I mention them a lot, but haven’t really gone too far into the stat.

Today, we’re going to do that; What expected goals are, what they mean, what they don’t mean, and…. Is it good if a player is performing above their expected goals?

Then, most importantly, we’ll then see how that can relate to the hobby.

Quick FYI: What are Expected Goals?

Before I get too far into the weeds here. I’ll quickly go over expected goals. There’s a lot of info online if you want to know more… but this is a soccer card newsletter, not a advanced soccer analytics newsletter… so I’ll keep it somewhat to the point.

Basically, expected goals (xG) is how likely a shot will result in a goal based on some characteristics of the lead-up, and the shot itself.

Every shot taken is lined up against thousands of shots with similar characteristics to determine the probability that this shot will result in a goal.

That probability of scoring as an expected goal total.

So, an xG of 0 is will almost always miss, while an xG close to 1 is a certain goal.

A lot of xG is based on the location of the shot. The further out a shot is, the less likely it is to go in. It also has a lot to do with the angle of a shot. For example, check this super accurate and mathematically correct visual representation I just drew in MS Paint…..

The green shot (directly in front) has a wide-open angle to shoot between the posts, this makes it way easier to score.

On the other hand, while the purple shot point is closer than the orange shot, the incredibly tight angle of the purple shot location means that it’s actually a lower value shot than you’d think….

There are a bunch of other factors that models use to calculate xG too. For example:

Where the defender is
The body part scored with (headed goals are way lower-value chances than with the foot)
The action before the shot. For example, receiving a cut-back pass, or a through pass is usually a higher value shot.
Was it an established attacking move? A quick rebound where the defense didn’t have time to re-group?

Each model for xG is somewhat unique, as some will use certain factors while others don’t.

All in all though, results aren’t usually drastically different.

It’s still a somewhat new statistic and there’s people all over the world working on getting it as accurate as possible.

Like I said, there’s a heap of detailed info out there if you want it. But that should be enough get the basics.

Players Performing Over Expected Goals This Season

Using data from fbref, here are the top twenty players performing above their expected goals.

NOTE: For all tables in this article, I’m using non-penalty goals and xG. That gives a way more balanced look. This is called np:G-xG (rolls off the tongue doesn’t it)

Some of these names you can instantly dismiss. For example, Kurt Zouma has scored a few headers that’s bumped his numbers up.

To me, these are players that stand out in this list (with links to their cards on eBay):

Why Do Players Perform Above Their Expected Goals? The Good, Bad, and Ugly.

There are plenty of reasons that players perform above their expected. Some good, some not so good. Here we’ll look at a few of them.

Two-Footed Players

An underrated reason some players perform xG (in my opinion) is if they’re two-footed.

Let’s look at Son Heung Min for example. Son is a great example of the type of player that almost breaks the expected goals model when he’s playing well.

Mainly because he is so comfortable using either foot when finishing.

Just check out this great finish from last week. Through ball. One-on-one with the keeper. Right foot. Easy goal.

But according to Wyscout, that’s only an xG of 0.1, meaning it’s only a 10% chance of scoring. I don’t know about you… but to me, that looked like it had no chance of missing.

Anyway, here’s another recent goal of his. This one on his left. Again, he hardly looks like missing this one.

A player that is so good at finishing with either foot should outperform their Expected Goals if they’re playing well.

Think about it…. every shot that is in the perfect spot for a right-footer is usually the exact opposite for a leftie - and the other way around.

Headed Goals

Like we touched on briefly before, headed goals are usually lower-value in expected goals than a shot from the same location with a foot.

There are few good reasons for this.

Headed shots are less powerful
They come in harder, usually contested possessions
They’re often from crosses and lobbed passes
They’re harder to control

However, if you’ve got a player that’s dominant in the air and looks to finish with their head, that’s can be a massive advantage.

Dominic Calvert-Lewin is that type of player. Just check out the goal he scored for England.

An awesome run, and incredibly well-timed with only one thing on his mind. The defender had absolutely zero chance there.

But still, how often do we see players miss open headers on goal?

All the time!

Being able to put those away means you’ll often perform above your expected goals.

Some Strikers Are Just Really Fucking Good

Finally…. some guys are just really fucking good at soccer.

If a player is constantly (I mean over years) performing above their expected goals, it’s probably not a fluke.

To go straight to the top, from the 2015-16 season onwards, Lionel Messi has scored 257 career goals off of 200 expected goals.

Per 90, that’s an xG of 0.66 while scoring 0.84 goals…. Needless to say, you’d expect Messi to outperform his his xG.

The same goes for Robert Lewandowski, since 2015-16 he has averaged 0.76 xG per 90 minutes, while scoring 0.91 goals per 90.

They’re just two examples from the very best players on the planet, but as you can see… Even the cream of the crop will only perform at about 20% above their expected goals over a large sample.

The Down Side…

One not-so great thing that could happen with a player that’s over-performing their expected goals is that there’s every chance they’ll revert back to the mean.

In other words, they’ll start to perform closer to their expected goals.

For example, here are players that performed highest above their expected goals last season.

There are some top strikers on that list that have beet great for a while.

To me, it’s not a huge surprise to see these guys on a list like this. They’re some of the best attacking players in the game and have been for a while. They’ve proven it over a decent to long period of time.

Sure, you could deep-dive every players’ career stats and get a better idea. But to me, there’s no real red flags there.

I did find it a little funny to see Sterling there though. He often gets a bad wrap as a poor finisher when it simply isn’t true.

The names that were curious to me as potential red-flags were:

Three young guys that were yet to prove it long-term.

Actually, to be honest, I wasn’t really concerned about Haaland. From what I’d seen he was a beast. However Greenwood and Sancho did stand out.

I was pretty vocal in the off-season that Mason Greenwood would probably revert closer to the mean and start to perform closer to his xG… Those numbers were unsustainable.

And that’s exactly what’s happening so far. This season he’s slightly under xG, with three goals from 3.15 xG.

The same goes for Sancho. He’s now sitting on five goals for the year off of 5.5 expected goals.

I wouldn’t stress about that too much at the moment though. They’re both scoring at the rate you’d expect him too. They’re still top prospects.

However, you should look a little deeper at a player’s underlying numbers when they are scoring well.

Players Who Underperform Their Expected Goals

The same way we take players overperforming their expected goals as a sign that they’ll eventually regress, we can take players that are underperforming and predict that some will eventually start scoring.

For example, here are the players that are underperforming their non-penalty xG by the largest margin this season.

To me, the obvious progression candidates that stand out are:

Funnily enough, Roberto Firmino underperformed his expected goals last season too. So I’m waiting and seeing what happens there.

However, all xG isn’t created equal when you look at large samples. It’s one of those things where for quarters don’t always equal a dollar.

You can have a bunch of terrible shots that, over time, add up to a decent xG… but as a series of individual shots, they’re not good.

To work around that, you can use a player’s expected goals per shot. Which is basically their expected goals divided by their total shots. Here is the same graph with that data included.

When you add in the expected goals per shot, you can get a clearer picture. For example, Moses Simon should be averaging a goal every five shots, which would put him on four goals instead of two.

The Impact for Collectors

Okay, I know what you’re probably thinking…..

Here is the impact of xG on the hobby.

Looking at a player’s goals (even against xG) is a great way to show how a player has performed… but not always the best way to predict future performance.

Just because a player is scoring well, doesn’t mean that they’re likely to continue to do so.

Check their expected goals. Are they performing 50% above their xG or something crazy like that?

Well, considering the absolute best in the world perform at about 20% above xG, it’s pretty unlikely that they will continue that form long-term.

Don’t expect a five-year hold on a young guy because they scored 10 goals in their first sixteen games off of 4 xG.

I’d expect players like Son to regress a little in his goal scoring as the season goes on. However, I do still expect him to perform above xG for the rest of the season…. His two-footed finishing along with Tottenham’s style of play will help that.

You can use the same strategy in reverse for players underperforming xG. There are some quality guys who are scoring less than their xG this season:

I’d expect all of these guys to start getting on the score sheet more as the season goes on.

Also, don’t stress too much if you have a player that is reverting back to the mean. The ceiling isn’t collapsing. Greenwood and Sancho are still top young players…. They were just performing at an unsustainable level.

Granted, that doesn’t help if you bought in the offseason….

Finally, you can also use xG to work out when might be a good time to sell. If a player is overperforming his xG by some unsustainable amount, it might be a good time to hop off.

That’s a personal decision though, and you should use more than one statistic to make it.

Final Thoughts

Expected goals isn’t the be all and end all. However, it is a great data point to see a player’s true performance.

You can also use xG to help you make decisions when buying and selling.

Your Next Steps

Subscribe if you haven’t done so yet

Share this with a friend in the hobby (or on your socials - make sure you tag me in too!)

DM me in Instagram @soccercardsrock or leave a comment below
Make sure you click through to those eBay links if you’re interested in buying anytime soon!

Soccer Cards Rock