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Why it is difficult to detect an illegally bowled cricket delivery with either the naked eye or usual two-dimensional video analysis
  1. K D Aginsky1,
  2. T D Noakes2
  1. 1Centre for Exercise Science and Sports Medicine, University of the Witwatersrand, Johannesburg, South Africa
  2. 2International Cricket Council (ICC) Accredited Testing Centre for Suspected Illegal Bowling Actions in Cricket, MRC/UCT Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, The University of Cape Town and the Sports Science Institute of South Africa, Cape Town, South Africa
  1. Correspondence to Dr Kerith D Aginsky, PO Box 29332, Sandringham 2131, South Africa; kerith.aginsky{at}


Objective 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.

Design Descriptive study

Setting One male bowler who had a large ℌcarrying angleℍ 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.

Main outcome measures 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.

Results The elbow joint rotates about 90° 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.

Conclusion It is impossible for an umpire conclusively to cite a bowler for an illegal action based only on naked eye observation. To do this the umpire would need to be in at least three different positions throughout a single delivery. Similarly, video footage shot from at least three different angles during the bowler's delivery action would need to be viewed by the match referee. By viewing the delivery from only one position, the visual illusion of a “throw” will be created by the presence of a large “carrying angle”.

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  • Funding The research undertaken in the unit was funded by the Harry Crossley and Nellie Atkinson Staff Research Funds of the University of Cape Town, the Medical Research Council of South Africa, Discovery Health, Bromor Foods and the National Research Foundation of South Africa through the THRIP initiative.

  • Competing interests None.

  • Patient consent Obtained.