Sports Rules MCP Server

Work an offside call through the published decision procedure — association football under IFAB Law 11, or ice hockey under NHL Rule 83 — and return every step, not just the verdict. Use this for any "was that offside" question in either sport. The two rules are structurally OPPOSITE and are routinely conflated, and there are four specific things that get answered wrong: SOCCER: 1. HANDS AND ARMS DO NOT COUNT, for anyone including goalkeepers. Only parts that could legally score are measured, and the boundary is the bottom of the armpit. This tool REFUSES to compute from an arm position rather than guessing where the shoulder was. 2. AN OFFSIDE POSITION IS NOT AN OFFENCE. It becomes one only with involvement in active play. Do not report "he was offside" when the answer is that he was in an offside position and uninvolved. `involvement` is REQUIRED once the geometry makes it decisive — the tool errors rather than assuming, so ask the user what the player actually did, and pass "none" if the answer is nothing. 3. No offside offence direct from a throw-in, goal kick, or corner. Absolute. 4. A DELIBERATE play by an opponent resets it; a deflection or a save does NOT. This is the distinction most arguments turn on. HOCKEY: 5. SKATES decide it. Not the stick, not the body. 6. Since 2021 a skate in the AIR above the blue line is still onside — the line is a plane, and ice contact is irrelevant. BUT this does not apply to tagging up on a delayed offside, where the skate must contact the line. Do not generalise the 2021 change to tag-ups. Input for soccer: positions along the attacking axis in metres, larger being nearer the opponents’ goal line — `attacker`, `ball`, `secondLastDefender`. Any consistent scale works; only the order matters. Optionally `restart`, `foremostPart`, `inOwnHalf`, `involvement`, `lastTouch`. Input for hockey: `rearSkate` in centimetres relative to the LEADING EDGE of the blue line, negative being the neutral-zone side. Optionally `skateOnIce`, `situation` (zone-entry or tag-up), and `stick`. Returns: a verdict of offside, onside, or no-offside-offence — three outcomes, not two, because "in an offside position but no offence" is a real and common answer — plus every step with the decisive one flagged, warnings, and a disclaimer. THIS IS NOT AN OFFICIAL RULING. Relay the steps, not just the verdict: in a real call the procedure is the easy half and the inputs are the argument. Do not quote IFAB or NHL rule text; it is copyrighted and this tool does not reproduce it.

Return the structural differences between soccer offside and hockey offside, dimension by dimension. Use this when someone asks how the two compare, or when you are about to reason about one sport using an intuition from the other — which is the commonest way to get either wrong. They differ on what part of the player is measured, when the picture freezes, whether position alone is an offence, what happens at exactly level, what resets the situation, and which restarts are exempt. Takes no arguments. Returns the comparison table.