['In this study, the influence of various anatomical and biomechanical factors on the ability to detect the magnitude of elbow extension during the cricket bowling action, with either the naked eye or from conventional two-dimensional video footage was evaluated.', 'Descriptive study', 'One male bowler who had a large carrying angle was studied by means of a three-dimensional biomechanical analysis using the Vicon MX13 motion analysis system when bowling at match pace. Photographs were taken from various angles during the bowling delivery action to illustrate factors influencing the visual appearance of an illegal delivery.', 'The influence of extension of the elbow joint and the elbow\'s anatomically fixed position, known as the "carrying angle", on the visual perception of an illegal ("thrown") delivery were the main outcome measures.', 'The elbow joint rotates about 90 degrees as a result of humeral rotation during the movement of shoulder circumduction produced by the bowler\'s delivery action. This causes the plane in which the elbow joint moves to change throughout the delivery action. This movement will also vary between bowlers. The movement of elbow planar flexion/extension can be viewed only when the viewer\'s eyes are at exactly 90u to the plane of elbow joint movement. Thus, a cricket umpire wishing to detect elbow extension during the bowler\'s delivery action would need continuously to change his viewing position as the bowler\'s arm moved from the horizontal to the vertical position at ball release. We show that by viewing the action from only one position, the umpire will be confused by the illusion of a "throw" produced by a large "carrying angle" in some bowlers.'] Is why it difficult to detect an illegally bowled cricket delivery with either the naked eye or usual two-dimensional video analysis?