FlagLine Offside Lab

FlagLine Offside Lab turns offside from a fuzzy sideline argument into a visual geometry skill you can practice anywhere—no signal, no account, and no dense rulebook on the touchline.

Built for youth assistant-referee trainees, high-school players, parent-coaches, and new center officials who must judge the line under pressure. Place attackers, the second-last defender, teammates, and the ball on a true half-pitch grid. The app draws a live offside line, grades edge cases, and explains the outcome in plain English.

GEOMETRY LAB Drag and drop up to 11 attackers or defenders plus the ball on a true-scale half-pitch. Snap players to lanes, flip attack direction, and watch the offside line redraw live with distance-to-line readouts and a clear ON, OFF, or WAIT verdict chip.

EDGE-CASE BENCH Toggle structured ruling cards for interfering with play, interfering with an opponent, gaining an advantage, deliberate play (including deflections), goalkeeper hand or arm involvement, and exemptions on throw-in, corner, and goal kick. Each card shows a mini diagram you can promote into the full lab.

50+ SEEDED FREEZE-FRAMES Browse scenarios tagged by topic—tight shoulder, late runner, keeper parry, defender header, free-kick wall rebound, goal-kick exit—and by age band from youth through adult. Fork any pack item into your own editable copy.

DECISION MODE Reveal a frozen pitch without the answer, choose Onside, Offside, Play-on, or Wait-and-see within a soft countdown, then unlock a plain-language rationale, the correct IFAB-aligned principle, and a one-tap restage in Geometry Lab.

SCENARIO EDITOR Name the frame, place players and ball, attach the intended correct call and a short coach note, save into personal packs, and reorder packs for self-study before a course or match weekend.

RUN-THE-LINE GUIDE Interactive touchline path showing where an assistant should stand relative to the second-last defender, when to drop and sprint, signal sequence, and large-type rainy-day cue cards for pre-match briefing.

EXPORT, WIDGETS, AND ACCESSIBILITY Export a printable PDF cue sheet with scenario thumbnails, correct calls, and personal notes via the system share sheet. Pin a Home Screen widget that shows a daily seed scenario prompt plus your last Decision Mode accuracy summary. Dynamic Type, high-contrast pitch themes (light stadium or dark night match), and yards or meters are supported in Settings.

ONBOARDING THAT TEACHES Walk a short onboarding that teaches the second-last-defender rule with three animated half-pitch demos, then pick your role persona—assistant-ref trainee, player, or parent-coach—to bias default scenario packs.

PRIVACY BY DESIGN Everything persists in on-device storage. No accounts, no network required, no player contact data, and no analytics resale. A seeded-content reset never wipes user-created packs without confirmation.

Turn offside into a repeatable visual skill—live line math, graded freeze-frames, edge-case rulings, and sideline cue cards that work with zero signal.