Place the line, grade the edge case, and call it under pressure—live half-pitch geometry for assistant-ref trainees, players, and parent-coaches who can’t re-open IFAB on the touchline.
Illustrative marketing figures; not App Store metrics.
Gallery frames from the lab, edge-case bench, and Decision Mode pressure reps.
Six tools that stay on the pitch with you — no PDF hunt, no account wall.
Drag up to 11 players plus the ball, snap to lanes, flip attack direction, and watch the offside line redraw live with distance-to-line numbers and a clear verdict chip.
Toggle cards for interference, advantage, deliberate play, keeper involvement, and throw-in/corner/goal-kick exemptions—each with a mini diagram you can promote into the full lab.
Browse scenarios tagged by trap and age band, then fork any frame into an editable personal copy for course night or match weekend self-study.
Call Onside, Offside, Play-on, or Wait-and-see on a hidden answer under a soft countdown, then unlock the IFAB-aligned rationale and restage the same frame in the lab.
Interactive touchline path for shoulder position, drop-and-sprint recovery, flag sequence to the center, plus rainy-day large-type cue cards for pre-match briefings.
Export printable PDF thumbnails with calls and notes via the share sheet, and pin a Home Screen widget with a daily seed prompt and your last Decision Mode accuracy—zero signal required.
FlagLine Offside Lab is an offline-first offside workbench built for people who must judge the second-last defender in real time. Drop attackers, defenders, and the ball on a true-scale half-pitch grid; the app redraws the offside line live, surfaces ON / OFF / WAIT verdicts with distance readouts, and walks edge cases—interfering with play or an opponent, gaining an advantage, deliberate play and deflections, keeper hand/arm, and restart exemptions—in plain English.
Seeded packs cover tight shoulders, late runners, keeper parries, and free-kick rebounds; fork any freeze-frame into your own pack, run timed Decision Mode, and study the run-the-line path with large-type cue cards. Everything stays in on-device SwiftData—no accounts, no network, no player contact data.