Thursday 21 February 2019

The Name Game.

Sports analytics, not just football (or soccer) has always had a problem when naming their metrics (see what I mean).

Corsi, TSR, Pythagorean and expected goals may work fine in a closed environment, but try sticking those terms into the mainstream and you're immediately on the back foot.

Jeff Stelling's rant wouldn't have been half as effective if he'd had to say "Chance quality, what's that!"

Anyway, we've already embarked on a second phase of attaching names to a brand new raft of models and performance indicators, except this time everyone's going to be scratching their heads about what it is that we're actually talking about.

Anyone who's ever posted an xG figure will be familiar with the "X get Y for their xG, why the difference" but the rise of the NS xG model will take that to new heights.

Shot based xG models (actually shots, headers and other body parts) all share a core set of inputs (location, type) and any additions simply move the dial slightly, but the steady onset of so call "Non Shot xG" models may lead to comparisons between models that bear very little relationship to one another.

538 has a NS xG model, defined thus,.

Non-shot expected goals is an estimate of how many goals a team could have scored given their nonshooting actions in and around their opponent’s penalty area.

Infogol has a NS xG model, but ours is based on the expected outcome of possession chains.

They currently share a name, but nothing else.

In an increasingly monetized situation it is understandable that some are reluctant or unable to share detailed descriptions of each model's makeup.

But, even if we can't avoid falling into the trap of using less than intuitive language to name commonly used metrics (as happened with xG), we perhaps should steer clear of using catch all terms, such as NSxG to describe future modelling efforts.

538's model appears to be event based, ours is possession based, so it's probably best to include this additional piece of information when presenting any NSxG models in the future. 

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