$npx -y skills add withqwerty/nutmeg --skill learnLearn about football analytics concepts and explore provider documentation. Use when the user asks what a metric means (xG, PPDA, expected threat, xT), wants learning resources, papers, or courses, is new to football analytics, or wants a learning path. Also use when the user ask
| 1 | # Learn |
| 2 | |
| 3 | Teach football analytics concepts, recommend resources, provide a learning path, and answer questions about data provider documentation — all adapted to the user's level. |
| 4 | |
| 5 | ## Accuracy |
| 6 | |
| 7 | Read and follow `docs/accuracy-guardrail.md` before answering any question about provider-specific facts (IDs, endpoints, schemas, coordinates, rate limits). Always use `search_docs` — never guess from training data. |
| 8 | |
| 9 | ## First: check profile |
| 10 | |
| 11 | Read `.nutmeg.user.md`. If it doesn't exist, tell the user to run `/nutmeg` first. |
| 12 | |
| 13 | ## Glossary of core concepts |
| 14 | |
| 15 | ### Chance quality metrics |
| 16 | |
| 17 | | Metric | What it means | Intuition | |
| 18 | |--------|--------------|-----------| |
| 19 | | xG (Expected Goals) | Probability a shot results in a goal (0-1) | "How good was the chance?" | |
| 20 | | xGOT (xG on Target) | xG adjusted for shot placement in the goal | "How good was the finish?" | |
| 21 | | xA (Expected Assists) | xG of the shot that resulted from a pass | "How good was the chance created?" | |
| 22 | | xT (Expected Threat) | Value added by moving the ball to a more dangerous area | "How much did this pass/carry increase goal threat?" | |
| 23 | | PSxG (Post-Shot xG) | Same as xGOT. StatsBomb terminology. | |
| 24 | |
| 25 | ### Possession and pressing |
| 26 | |
| 27 | | Metric | What it means | |
| 28 | |--------|--------------| |
| 29 | | PPDA | Passes allowed per defensive action. Lower = more pressing | |
| 30 | | High press | Defensive actions in the opponent's defensive third | |
| 31 | | Counterpressure | Immediate defensive reaction after losing the ball | |
| 32 | | Build-up | How a team progresses the ball from defence to attack | |
| 33 | | Possession value | How much each action contributes to scoring probability | |
| 34 | |
| 35 | ### Passing |
| 36 | |
| 37 | | Metric | What it means | |
| 38 | |--------|--------------| |
| 39 | | Progressive pass | Pass that moves the ball significantly toward the opponent's goal | |
| 40 | | Key pass | Pass directly leading to a shot | |
| 41 | | Assist | Pass directly leading to a goal | |
| 42 | | Through ball | Pass played into space behind the defence | |
| 43 | | Switch of play | Long pass crossing the centre of the pitch | |
| 44 | | Pass completion % | Successful passes / total passes (misleading in isolation) | |
| 45 | |
| 46 | ### Shooting |
| 47 | |
| 48 | | Metric | What it means | |
| 49 | |--------|--------------| |
| 50 | | Shots per 90 | Shot volume normalised by playing time | |
| 51 | | Conversion rate | Goals / shots (noisy, small sample issues) | |
| 52 | | Big chance | High-xG opportunity (typically xG > 0.3) | |
| 53 | | Shot on target % | Shots on target / total shots | |
| 54 | |
| 55 | ### Defensive |
| 56 | |
| 57 | | Metric | What it means | |
| 58 | |--------|--------------| |
| 59 | | Tackles won | Successful tackle attempts | |
| 60 | | Interceptions | Reading and intercepting opponent passes | |
| 61 | | Clearances | Defensive clearances (often under pressure) | |
| 62 | | Blocks | Blocking shots or passes | |
| 63 | | Aerial duels won | Headers contested and won | |
| 64 | |
| 65 | ### Per-90 normalisation |
| 66 | |
| 67 | Always normalise player stats per 90 minutes, not per match: |
| 68 | ``` |
| 69 | per_90 = (raw_stat / minutes_played) * 90 |
| 70 | ``` |
| 71 | |
| 72 | Why: a player with 2 goals in 180 minutes (per 90: 1.0) is performing the same as one with 1 goal in 90 minutes. Per-match stats penalise part-time players. |
| 73 | |
| 74 | **Minimum sample:** ~900 minutes (10 full matches) before per-90 stats are meaningful. |
| 75 | |
| 76 | ## Learning path |
| 77 | |
| 78 | ### Stage 1: Getting started |
| 79 | |
| 80 | 1. **Read:** "The Numbers Game" by Chris Anderson and David Sally. Accessible introduction to football analytics. |
| 81 | 2. **Watch:** Tifo Football YouTube channel for visual explainers of tactical and analytical concepts. |
| 82 | 3. **Do:** Load StatsBomb open data and make a shot map. Just plot the x,y coordinates of shots, colour by goal/no goal. |
| 83 | 4. **Understand:** What xG is and isn't. Read StatsBomb's public xG methodology. |
| 84 | |
| 85 | ### Stage 2: Building skills |
| 86 | |
| 87 | 1. **Read:** "Soccermatics" by David Sumpter. Mathematical modelling applied to football. |
| 88 | 2. **Learn:** How to make pass networks and xG timelines. |
| 89 | 3. **Practice:** Analyse a full match. Write up what happened and what the data shows. |
| 90 | 4. **Explore:** FBref for season-level stats. Compare teams across multiple dimensions. |
| 91 | 5. **Tool up:** Learn pandas/polars (Python), tidyverse (R), or D3.js (JavaScript) for data manipulation and visualisation. |
| 92 | |
| 93 | ### Stage 3: Going deeper |
| 94 | |
| 95 | 1. **Read key papers:** |
| 96 | - Decroos et al. (2019) "Actions Speak Louder than Goals" (VAEP model) |
| 97 | - Fernandez & Bornn (2018) "Wide Op |