Throwing (cricket) - Biomechanics and Modifications To The Throwing Laws

Biomechanics and Modifications To The Throwing Laws

Testing conducted in the 1990s in England revealed that during a delivery virtually all bowlers flex and extend their arms naturally to some degree as it rotates around the shoulder. This testing revealed that the strict Laws of Cricket which banned any flexing of the arm were impossible to follow. At this time a set of tiered tolerance thresholds for the amount of allowable elbow extension, or straightening, were implemented: 10 degrees for fast bowlers, 7.5 degrees for medium pacers, and 5 degrees for spin bowlers. Enforcing these new measures proved problematic, as the laboratory based measurement systems used had a margin of error of at least 1 degree, and video based measurement systems were likely to have more, especially if inappropriately executed.

A later study from 2000-2003 showed that bowling actions that looked normal to the naked eye in many of the worlds elite fast bowlers, had, on average 9 degrees of elbow extension during the bowling action. Some recorded elbow extension measuring between 10-15 degrees, yet none of these bowlers had ever had a problem regarding the legality of their bowling action. This testing showed that a zero tolerance threshold, and the tiered thresholds implemented in the late 90's, had no or little scientific merit. The study, conducted by the Australian Institute of Sport Biomechanics department, lead by cricket biomechanist Dr. Marc Portus, involved taking three-dimensional video based biomechanical analyses during tour, test and one-day international matches in Melbourne, Sydney and Brisbane. Results from this work indicated that video based measurement error in such a scenario, using best practice methodologies, was 3 degrees. This report was submitted to the ICC in 2003, which instigated the review of the illegal action definition and processes.

Subsequent to this the ICC received data from laboratory based analyses, on the basis that these measurement environments are more controlled, involving more sophisticated measurement technologies such as the Vicon Motion Analysis system. These were subject to less measurement error. Data was provided by the Australian Institute of Sport, the University of Western Australia and the Motion Analysis Corporation system from the University of Auckland. The ICC also carried out further video based three-dimensional analyses on all bowlers during the 2004 Champions Trophy in England. Regardless of the biomechanical measurement protocol used, a strikingly similar pattern emerged: the normal biomechanics of cricket bowling, whether it be spin or pace, features an element of elbow extension. The average extension of a normal, seemingly legal delivery was 8-10 degrees for all bowler types. There were virtually zero instances of no elbow extension at all in accordance with the original laws.

The ICC formed an expert panel comprising biomechanists Professor Bruce Elliott of The University of Western Australia, Dr Marc Portus of the Australian Institute of Sport and Dr Paul Hurrion from the UK who presented during a forum of a special ICC cricket sub-committee for illegal bowling actions in late 2003 in Dubai. The sub-committee was David Richardson, Angus Fraser, Aravinda De Silva, Michael Holding, Tony Lewis and Tim May. After this meeting the ICC decided to raise the elbow extension tolerance threshold to 15 degrees for all bowlers. This limit was chosen after considering biomechanical findings from 130 pace and spin bowlers, the scientific issues with measurement, and that bowling actions considered to be "throw-like", or illegal, were usually measured to be well above 15 degrees of elbow extension, often in the 20 to 30 degree range.