OffsideFlag
The referee's kit made smart: flags that buzz the wrist, an 8-second keeper count, a sin-bin board the benches can read, a playing-time board for youth leagues, and a body camera that records abuse only when the official says so
Replaces the pair of plain flags a referee crew already carries with flags whose grip buzzes the referee's wrist, runs the 8-second goalkeeper count (Law 12) on the wrist unit, and turns the chest LineCam into RefCam: a body camera for the lone grassroots referee that records only when the referee presses REC, shows a red light so players know, and seals each clip for the county FA. UmpCam puts the same camera on a belt clip for baseball and softball umpires, marks ejections and drafts the 24-hour ejection report. SinBin adds an e-paper board on the halfway flag post: the referee logs a sin bin with a triple press on the wrist, starts it at the restart, pauses it for lost time and half-time, and both benches see each player's time left. QuarterBoard (rev A5) straps under it for youth leagues with "everyone plays" rules: the coaches send each quarter's starters from their phones, the referee's press at the quarter kick-off locks them, and the board shows quarters played and who must start next, so the referee can warn a coach before the rule is broken.
- Who buys it
- County FAs, leagues and referee associations running body-camera schemes (the FA trial and Football Victoria each started with about 100 referees), plus adult amateur referees who buy their own kit; plain flags cost $30–$51, beep-flag sets $899.95 (ErvoCom), grassroots body cameras about £89.99 and evidence-grade ones about $1,065. In baseball and softball: state associations with body-camera pilots (WIAA, 100 cameras), umpire assignors and tournament directors.
- Why it pays
- RefCam is about $121 of parts per referee (est.), the price of a basic grassroots camera, but with the encryption, warning light and 60-day deletion a league's data rules ask for, without $41 per camera per month of fleet software (est.). Beep-flag Set target $249 against $899.95.
- Target price
- $249 OffsideFlag Set (2 flags + wrist unit), $99 SinBin board, $119 QuarterBoard, $199 per LineCam, RefCam or UmpCam, $599 Crew Kit (target)
- First-minute wow
- A player squares up to the referee; the referee says "I'm recording" and presses REC; a red ring lights round the lens, the wrist buzzes, and the clip is already sealed for the county FA, out of reach of the referee, the clubs and social media.
What the research found
And how this design answers it
- AYSO youth soccer credits a quarter to the player who starts it (an injury sub gets none), referees mark A for absent and I for injured (counts as played), and must warn a coach whose substitutions will break the playing-time rule (AYSO National: half a game; Region 76: 3 of 4 quarters, keepers max 2 quarters in goal at 10U; late after the 2nd quarter owes 1) or face points off or a forfeit → QuarterBoard: a 4.2 in e-paper board strapped under the SinBin board; coaches send each quarter's starters from their phones, the referee's press at the quarter kick-off locks them, the board shows every shirt number with quarters played and MUST START, and buzzes the referee if a lineup leaves a must-start player out; engine 5/5 rule checks; about $62 of parts (est.)
- FA grassroots sin bins are mandatory up to Step 5 and in youth football: 10 min (8 in shorter games), started at the restart, lost time added, carried over half-time, return only when the ball is out and the referee allows it, and county FAs tell lone referees to note each minute and do the sums (Birmingham FA: binned 25/33/41 → back 35/43/51) → SinBin: a triple press on the wrist logs it, the next press starts it, a 2 s hold pauses all timers; an e-paper board strapped to the halfway flag post shows HOME/AWAY time left to the benches and buzzes the referee when a period is served; engine 5/5 rule checks; about $53 of parts (est.)
- Baseball and softball umpires take abuse from coaches and parents (baseball 20 of 89 Washington high-school ejections in 2022–23) and must file an ejection report within 24 h (MPSSAA, GHSA) or 48 h (Softball BC); the WIAA/Reveal pilot keeps a 30 s loop saved on a press after showing the camera at the pre-game meeting, and umpires taping action cameras to masks report 2 h batteries, endless dead footage and hard apps → UmpCam: an ump-belt-clip puts RefCam on the umpire belt (no chest harness under a chest protector), 30 s RAM pre-roll only where policy allows, a 2 s press marks EJECTION and the phone drafts the report with the clip hash before the deadline; audio off (Little League microphone rule); UmpCam about $109 of parts (est.)
- Grassroots referees work alone and take the abuse (1,451 serious-offence allegations against officials in 2022–23, FA), and the FA's IFAB-approved trial and Football Victoria's 2025 scheme give them body cameras that record only for threats or serious misconduct, after telling players, encrypted and deleted within 60 days → RefCam: a refcam-lid with a guarded REC key, a red halo round the lens, camera off until pressed, clips encrypted to the county FA key and deleted at 60 days; +$0.70 BOM (est.)
- Since July 2025 a keeper holding the ball over 8 s concedes a corner and the referee must count 3 s silently then the last 5 on a raised hand (IFAB Law 12; NFHS interpretation 2026), on top of watching play → the KeeperCount lid adds a guarded thumb button to the wrist unit; it buzzes at 3 s, ticks 4-7 and long-buzzes at 8, pauses on a press if an opponent blocks the release, and logs each count; +$0.35 BOM (est.)
- Electronic beep flags cost $725–$900 a set, so grassroots crews use plain flags and the referee misses signals while facing away → an ESP32-C3 grip and a wrist unit give the same buzz for a $96 BOM (est.)
- About 1 in 4 offside flags at a World Cup were wrong (26.2%, Helsen 2006), mostly from the flash-lag effect, and position off the line adds parallax → the CAD report shows an AR 1 m off the line sees a level attacker 3 m off when the attacker is near and the defender far; the LineCam records that view so assessors can coach positioning instead of arguing
- Club linesmen are partisan, so referees limit them to ball-out signals → the flag still helps (the referee feels a ball-out flag they cannot see), and the LineCam is sold for neutral ARs
Use case
Abuse after a penalty in a Sunday league match, referee alone
RefereePlayersCounty FA disciplinary officer
- 01Trigger: a player and a substitute surround the referee after a penalty, swearing and pushing forward
- 02Detection: the referee says "I'm recording" and presses REC on the chest RefCam (or double-presses the wrist key)
- 03Alert: the wrist buzzes once and the red halo blinks for 3 s, then glows while it records, so everyone can see it
- 04Action: the clip is encrypted on the card, uploaded to the county FA after the match and attached to the misconduct report; the card copy deletes itself
Outcome: The disciplinary panel sees what happened instead of one word against another; nobody can post or edit the clip (est.)
How it works
Architecture
- 01
Sense: button and LIS3DH accelerometer in each flag grip; Camera Module 3 Wide on the chest (AR LineCam or referee RefCam); thumb buttons on the wrist unit and the RefCam lid; HOME and AWAY keys on the SinBin board
- 02
Decide: ESP32-C3 in the grip classifies press, raise and wave; the wrist unit runs the 8 s keeper count; RefCam keeps the camera off until REC, with no pre-roll unless the competition allows it; UmpCam can hold a 30 s RAM pre-roll where policy allows and a 2 s press marks an ejection; the wrist runs sin-bin timers that start at the restart and pause with the match
- 03
Send: ESP-NOW from flags and wrist to the cameras; after the match RefCam uploads sealed clips to the county FA over the referee's phone hotspot
- 04
Tell: wrist buzz and LEDs; a red halo on the RefCam while recording; a signed log of every clip's time and hash; the SinBin e-paper board shows each sin bin's time left and READY
Hardware
Real parts, buyable today
Bill of materials: about $97 per Set (2 flags + KeeperCount band), $52.28 per SinBin board, $61.58 per QuarterBoard, $120 per LineCam, $121 per RefCam, $109 per UmpCam, $337 per Crew Kit at qty 1 (est.).
| Block | Part | Why this part |
|---|---|---|
| Flag grip | Seeed XIAO ESP32C3 + Adafruit LIS3DH + 18650 + 12 mm IP67 button in a Ø36 ASA grip | ESP-NOW with no pairing to Wi-Fi, a season of standby, the cell is also the grip's counterweight |
| Referee wrist unit | XIAO ESP32C3 + 500 mAh LiPo + coin motor, 22 mm strap | Felt, not heard, so it works in wind and crowd noise |
| KeeperCount button | C&K PTS645SM43 6 x 6 tact switch under a TPU cap in a guarded kc-lid | A firm press that a sleeve cannot knock; the TPU flange keeps it captive under the lid |
| RefCam REC key and light | PTS645 tact switch under a TPU key in a guarded refcam-lid, 3 red LEDs under a clear PETG halo | One deliberate press starts recording and players see a red ring from any side, as the scheme rules ask |
| Camera and compute | Camera Module 3 Wide + Raspberry Pi Zero 2 W + XIAO ESP32C3 | Hardware H.264 and on-card encryption to the FA's public key; hears the flags and the wrist key |
| LineCam power | 2000 mAh LiPo + PowerBoost 1000C | 3.9 h of recording or 9 h armed per charge (est.) |
| UmpCam belt clip | ump-belt-clip (ASA) with 3 GoPro fingers, M5 thumbscrew, lanyard tether | Drops over a 1.5–1.75 in umpire belt beside the ball bags; tilted 15° up so a coach's face is in frame from 0.6 to 2 m |
| SinBin board | Waveshare 2.9in e-paper + XIAO ESP32C3 + 18650 + 2 IP67 keys in a sinpost-case strapped to the halfway flag post | Readable in sun from the bench, holds the image with no power, 40+ matches per charge (est.) |
Mechanical
Printable CAD
16 parts, generated from code and checked as closed solids. Pick a part to inspect it, or download the STL files to print.
See the CAD parts render
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Bought hardware fitted inside this part (checked in the CAD: nothing collides with the plastic)
- Flag grip (button flat, electronics bore, tube socket), 2 per setgrip-body.stl · ASA
- Grip end cap with O-ring and lanyard loop, 2 per setgrip-cap.stl · ASA
- Referee wrist unit case with 22 mm strap lugsband-case.stl · ASA
- Wrist unit lid with left/right AR LEDs (rev A, no keeper button)band-lid.stl · ASA
- KeeperCount wrist lid: LEDs, guarded thumb button, switch sleeve (rev A1, replaces band-lid)kc-lid.stl · ASA
- KeeperCount TPU button cap with captive flangekc-button.stl · TPU
- LineCam case with GoPro-style fingers, 1 per ARlinecam-case.stl · ASA
- LineCam lid with camera standoffs and lens hoodlinecam-lid.stl · ASA
- RefCam lid: guarded REC key sleeve and 3 recording-LED holes round the lens (rev A2, replaces linecam-lid for referees)refcam-lid.stl · ASA
- RefCam REC key, TPU with captive flangerec-key.stl · TPU
- RefCam recording halo: clear ring round the lens lit by 3 red LEDsrefcam-halo.stl · PETG
- UmpCam belt clip: drops over a 1.5–1.75 in umpire belt, GoPro fingers for the RefCam case (rev A3, replaces the chest harness)ump-belt-clip.stl · ASA
- SinBin board case: e-paper, 18650, HOME/AWAY keys, saddle and strap tunnels for a 25–32 mm halfway flag post (rev A4)sinpost-case.stl · ASA
- SinBin board lid with window, acrylic cover recess and sun brow (rev A4)sinpost-lid.stl · ASA
- QuarterBoard case: 4.2 in e-paper, 18650, NEXT/OK keys, saddle and strap tunnels for the halfway flag post (rev A5)quarterboard-case.stl · ASA
- QuarterBoard lid with window, acrylic cover recess and sun brow (rev A5)quarterboard-lid.stl · ASA
Open risks we are working on
- Body cameras are a competition option, not standard Laws equipment: RefCam is used only where the county FA or league runs a scheme, under its protocol
- Filming minors: off in youth football unless the competition's safeguarding rules allow it
- A camera does not stop abuse by itself; trial results are referees' own reports, not controlled studies
- RefCam records conduct for disciplinary cases; it is never a review system and cannot change a match decision (Law 5)
- Encryption keys and uploads need each county FA to run a store; without one, clips stay sealed on the card
- Reveal-class body cameras and ReplAi-style grassroots cameras already sell to FAs; a cheap scheme camera could undercut us
- Baseball and softball rules are silent on umpire cameras: UmpCam needs the league or tournament's written policy, and players under 18 will appear in frame
- Sin-bin timing depends on the referee pressing at the restart and at stoppages; a missed press makes the board as wrong as a stopwatch, and the board cannot know shirt numbers
Design stage only: nothing on this page is for sale. Specifications and prices are targets.