Can a phone check whether a bowling action is legal?

Bowling-action legality concerns elbow extension during the relevant part of the delivery. That is a three-dimensional joint-motion question. The apparent bend in a two-dimensional image changes with camera position, upper-arm rotation, clothing, landmark visibility and the exact frames chosen for comparison.

• Depth is projected onto a flat image, hiding motion toward or away from the lens.
• A small camera-angle error can change the apparent elbow angle.
• Automatic pose landmarks estimate joint centres; they are not calibrated lab markers.
• Motion blur and an obscured arm can move the estimated wrist, elbow or shoulder.
• An official protocol controls capture, calibration, processing and review.

A clear clip can support an initial coaching conversation, document how the action looks from a particular view and help an athlete prepare questions for an appropriately accredited assessment. It can also analyse other observable patterns when the camera is suitable, such as delivery events, front-knee behaviour and release repeatability.

Speak with a qualified coach and follow the assessment process of the governing body under which you compete. Do not attempt to redesign an action around a number produced by an uncalibrated phone app, particularly when pain is present.

The ICC defines the 15-degree threshold and the accredited assessment process. Laboratory research shows that elbow motion and wrist speed interact in three dimensions, while a recent cricket-specific markerless system still showed important disagreement and missing trials against marker-based motion capture. Together, these sources support a strict boundary: phone video can describe a visible cue, but it cannot issue an official verdict.

1. International Cricket Council. Illegal Bowling Actions. Official guidance
2. Middleton, Alderson, Elliott & Mills (2015). The influence of elbow joint kinematics on wrist speed in cricket fast bowling. 10.1080/02640414.2014.1003586
3. Abraham, Feros & Fox (2025). Exploring the accuracy of OpenCap for three-dimensional analysis of cricket bowling. 10.1177/17479541251348081