Thread by @Soccermatics

Expected Threat (xT) is one of the most important (but least well-understood) statistics in football. ⚽️⚽️

It was used by Liverpool (they call it Goals Added) to do some of their best scouting. 📈

And now, YOU can learn all about it...🧵

The basic idea of xT is to assign a value to a position on the pitch or an action based on the probability it will lead to a goal.

It was proposed (ten years ago) by @srudd_ok who had the idea of using Markov chains to measure how much different parts of the pitch are worth.

This was a mathematically elegant solution and in this video I explain how xT (or probability of a goal) can be calculated step by step.

The name Expected Threat (xT) came form @karun1710, who also described how it works in this amazing interactive blog post. karun.in/blog/expected-…

Lots of different names --- EPV, OBV, G+, VAEP etc. --- have been given to the xT approach.

I distinguish between position-based xT (where place on the pitch is assigned value) and action-based xT (where passes, dribbles etc. are assigned value).

soccermatics.readthedocs.io/en/latest/less…

I start by explaining the position-based version of xT. By measuring transitions between different parts of the pitch and the probability of scoring from them, we can iteratively value different places on the pitch.

Then I turn to action-based xT, which better captures the dynamic nature of football.

We can assign value, not just to position, but also how we move between positions.

The action-based version of xT has not been presented in so much detail before, although it is better for professional applications.

I try to put this right in this video...

And @aleksander_and has done a wonderful step-by-step implementation here. soccermatics.readthedocs.io/en/latest/gall…

And I use the @twelve_football implementation of action-based xT to give application examples in this video.

I hope learning about xT is as much fun as it has been to write and make videos about.

And that you can make your own version🤗🤗

Enjoy!