Expected Goals (xG): what it is, and how VAIXR calculates it

Three shots on target, no goal, and yet it was a good first half. A 0-0 scoreline can't explain that feeling — xG can. Expected Goals estimates, per shot, how likely it is to become a goal, based on where and how the shot was taken. Add those probabilities up over a match and you get a number that's independent of luck or a good or bad goalkeeper: how many goals "should" have gone in.

That's exactly why xG has become the standard measure alongside the score in professional football. A team that loses 1-0 but builds 2.3 xG against the opponent's 0.4 played a different match than the final score suggests.

How VAIXR values a shot

Top clubs train their xG models on millions of shots from video data: exact angle, distance to goal, defender pressure. That data doesn't exist at amateur level, and that precision wouldn't help much between two training sessions anyway. So VAIXR uses a simple, transparent model built on three things you're already recording while tagging a shot:

• Distance to goal, in four zones: the 5-metre box, the near penalty area (5-11m), the far penalty area (11-18m), and outside the area (18m+). This sets the base value — from 0.45 right in front of goal to 0.03 from distance.
• Body part: a header or "other" (a shoulder, say) counts lower than a shot with the foot — a header is simply harder to place accurately.
• Type of action: a shot from a free kick or corner counts slightly lower (the ball arrives from the side or from a stationary position), a shot from a counter-attack counts slightly higher (the defence isn't set yet).

Those three factors are multiplied together into a single probability between 0.01 and 0.99. A header from a corner, say, from the near penalty area: 0.15 base × 0.65 (header) × 0.85 (corner) ≈ 0.08. A foot shot from close range on the counter: 0.45 × 1.00 × 1.10 ≈ 0.50 — close to a coin flip.

Where you'll see it

You don't need to do anything extra for it. As soon as you tag a shot's distance, body part and type of action — in the live tagger, on the touchline or afterwards — VAIXR calculates the xG value automatically. That value comes together in two places:

• Match statistics: at the top of every match's statistics screen, your own team's xG sits next to the opponent's xGA (expected goals against) — the total of every tagged shot in that match, for and against.
• Player monitor: on an individual player's page, cumulative xG counts as part of their stats, so a striker who gets plenty of good chances but hasn't scored yet shows up in the number, not just in a gut feeling.

That turns "we created little, but the chances we had were big" into something you can back with a number — and so does "he's had big chances three matches running, the goals will come".