# Sports Rules

Work an offside call through the actual decision procedure, for association football under IFAB Law 11 and ice hockey under NHL Rule 83. Applies the parts that get missed — the arm exclusion and the involvement test in soccer, the blue-line plane and the tag-up exception in hockey — and shows every step it took, so the answer can be argued with rather than just accepted.

**Not for:** Not an official ruling and not a substitute for a match official. This works through published decision procedures from the inputs you supply; it cannot see the play, and the hard part of a real offside call is almost always judging the inputs rather than applying the rule. Refereeing judgement, video review protocols, and competition-specific variations are outside what this models. Rule texts belong to IFAB and the NHL and are not reproduced.

## The two rules, side by side

| | Soccer — IFAB Law 11 | Hockey — NHL Rule 83 |
| --- | --- | --- |
| **What part of the player is measured** | The foremost part that could legally score — head, body or feet. Hands and arms are excluded for everyone including goalkeepers, with the boundary at the bottom of the armpit. | Skates, and only skates. The stick is irrelevant, and so is the body — a player can lean well over the line and stay onside. |
| **When the picture freezes** | The moment a TEAM-MATE plays or touches the ball. Not when the ball is received. | The moment the PUCK crosses the leading edge of the blue line. |
| **Is being in an offside position an offence?** | No. It is only an offence with involvement in active play: interfering with play, interfering with an opponent, or gaining an advantage. | Effectively yes. Preceding the puck into the zone is itself the infraction. |
| **What happens at exactly level, or on the line** | Level with the ball or the second-last opponent is ONSIDE. | A skate on, or above, the leading edge has not broken the plane, so ONSIDE. |
| **Does anything reset it** | Yes. An opponent who DELIBERATELY plays the ball resets the situation; a deflection, a save, or a rebound off the post does not. | Yes, but differently: a delayed offside can be negated by tagging up — every attacker clearing the zone — and there the skate must contact the line. |
| **Restarts it cannot happen from** | Throw-in, goal kick, and corner kick. Absolute, whatever the positions. | Not applicable — offside is about zone entry, not about the restart type. |

Rule texts belong to IFAB and the NHL and are not reproduced here. This is the decision procedure restated, with the governing body named.

## The four things usually got wrong

1. **Soccer: hands and arms never count**, for anyone including goalkeepers. The boundary is the bottom of the armpit.
2. **Soccer: an offside position is not an offence.** It needs involvement in active play. And there is no offence at all direct from a throw-in, goal kick, or corner.
3. **Soccer: a deflection does not reset offside.** Only a DELIBERATE play by an opponent does. IFAB gives five criteria for telling them apart, with no pass mark.
4. **Hockey: since 2021 a skate in the air is still onside** — the blue line is a plane, and ice contact is irrelevant. **But not when tagging up** on a delayed offside, where the skate must contact the line.

## Surfaces

- HTML: `https://sports-rules.gumballtools.com`
- Markdown: same URLs with `Accept: text/markdown` or `?format=md`
- JSON API: `https://sports-rules.gumballtools.com/api/v1/offside` and `https://sports-rules.gumballtools.com/api/v1/contrast`
- OpenAPI: `https://sports-rules.gumballtools.com/.well-known/openapi.json`
- MCP: `https://sports-rules.gumballtools.com/api/mcp`

Soccer positions are metres along the attacking axis, larger being nearer the opponents’ goal line; any consistent scale works. Hockey positions are centimetres relative to the leading edge of the blue line, negative being the neutral-zone side.

## Worked examples

- [Offside in soccer, step by step](https://sports-rules.gumballtools.com/offside/offside-in-soccer-explained) — Nearer the goal line than both the ball and the second-last opponent, and involved in play. Every step shown, including the ones that did not decide it.
- [Level with the last defender is onside](https://sports-rules.gumballtools.com/offside/level-with-the-last-defender) — The test is NEARER, not level. A striker exactly in line with the second-last opponent is on, which is why the tightest calls come down to a toe.
- [The shoulder counts, the arm does not](https://sports-rules.gumballtools.com/offside/shoulder-offside-but-not-the-arm) — Hands and arms are excluded for every player including goalkeepers, and the boundary is the bottom of the armpit. A shoulder in front can decide a call.
- [You cannot be offside from a throw-in](https://sports-rules.gumballtools.com/offside/no-offside-from-a-throw-in) — Nor from a goal kick or a corner. This is absolute, whatever the positions were, and it is the most commonly forgotten part of the law.
- [In an offside position, but not offside](https://sports-rules.gumballtools.com/offside/offside-position-but-no-offence) — Standing in an offside position is not an offence. Without involvement in active play there is nothing to penalise, and play simply continues.
- [A deflection does not reset offside](https://sports-rules.gumballtools.com/offside/deflection-does-not-reset-offside) — The ball coming off a defender feels like it should wipe the slate. It does not — only a deliberate play does, and that distinction is what the argument is usually about.
- [A deliberate play does reset it](https://sports-rules.gumballtools.com/offside/deliberate-play-resets-offside) — A defender who deliberately plays the ball hands it over, and receiving it is not gaining an advantage. IFAB gives five criteria for judging that, with no pass mark.
- [You cannot be offside in your own half](https://sports-rules.gumballtools.com/offside/offside-in-your-own-half) — However far ahead of the ball and the defence you are. Offside is a rule about the opponents’ half.
- [Offside in hockey, step by step](https://sports-rules.gumballtools.com/offside/hockey-offside-explained) — The attacking team must not precede the puck into the zone, and it is the skates that decide it. Not the stick, not the body.
- [A skate in the air is still onside](https://sports-rules.gumballtools.com/offside/skate-in-the-air-is-still-onside) — The 2021 change most explanations still miss. The blue line is a plane extending upward, and a skate that has not broken it is onside whether or not it is touching the ice.
- [Tagging up: where the in-air rule stops applying](https://sports-rules.gumballtools.com/offside/tagging-up-on-a-delayed-offside) — The exception inside the exception. To clear a delayed offside the skate must contact the blue line — being above the plane is not enough.
- [The stick across the line does not matter](https://sports-rules.gumballtools.com/offside/stick-across-the-blue-line) — A player can reach well into the zone with their stick, or lean over the line, and stay onside as long as the skates are back.
- [Soccer offside vs hockey offside](https://sports-rules.gumballtools.com/offside/soccer-vs-hockey-offside) — Same word, structurally opposite rules. What gets measured, when the picture freezes, and whether the position is itself an offence — all different.