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Decision Review System: Explaining the technology behind it

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Snickometer’s usage has been vastly reduced
Modified 10 Nov 2016

With technology taking over every aspect of life, it was only a matter of time before it is utilised to the advantage of sports. Technology in sport is used with an objective to eliminate human errors that may have earlier affected the course of the game drastically. The Decision Review System was introduced in cricket, to give the players an opportunity to review such errors from the on-field umpire.

The sequence of a typical DRS review involves checking for the front foot no-ball, bat edge detection and then ball tracking in the case of lbw appeals. The on-field umpire indicates the original decision and refers it to the third umpire, who makes uses of the available DRS tools before reaching a conclusion that may or may not stand by the on-field umpire’s call. ‘Available DRS tools’ is the keyword here, because the tools available to review a decision, at the moment, vary from series to series. 

Though the ICC has been advocating uniform application of the DRS in all international cricket played across the globe, hosting boards, especially the poorer among them, are often unable to afford the costs of hiring DRS technology and either choose to use it in parts or opt out fully.

Nevertheless, even when DRS is not involved, these tools are often employed by broadcasters to bring vivid analysis of these moments in the game to its followers. With India’s use of DRS making headlines and expected to play a major role in the series, there is an eagerness among the Indian fans to grasp the intricacies of it.

Also read: Decision Review System: India's journey with the DRS technology so far 

This is an attempt to explain to you, the different technological tools used in the Decision Review System


The Snickometer technology(Snicko) invented by British Scientist Allan Plaskett in 1990 combines sound and visual evidence to help the umpires determine whether a batsman has actually nicked the ball – especially in the case of caught behind, bat-pad and lbw appeals.

The stump microphone picks up the live sound, filters it and relays it to an oscilloscope attached to it, which then traces the relevant sound waves. In the meantime, cameras record the visual and replay it in slow motion.


If the ball is suspected to have hit the bat, the Snicko sound graph is checked for impact - a single, sharp spike on the graph will confirm the ball touching the bat. On the other hand, if it touches the pad or glove, a flatter impact is observed on it.  The sound is then correlated by the third umpire with the slow motion replays of the ball passing the bat to make his final decision.

This is especially the case when it’s a close call to make, with more than one genuine sound - bat hitting the ground, for example - and timing of each sound to be distinguished to determine the sound coinciding with the ball passing the bat. And, when there’s daylight between bat and ball, the graph stays undisturbed.

Although it was used earlier in UDRS, unlike Hawk Eye and Hot Spot, it is currently not used to that extent.
This is because, while the cost involved is the least – it requires the stump mic and camera only – the evidence obtained can be inconclusive and prone to dubious decision-making, and in recent years, more comprehensive and accurate technologies have taken its place.

Hot Spot

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Hot Spot technology

Hot Spot is a more accurate solution to detecting edges than the Snickometer as it is not a sound-based edge detection system. It was invented by French scientist Nicholas Bion and was first used in Australia on the Channel 9 network. Two cameras placed on opposite sides of the ground record the visuals and yield infra-red images. The principle behind the Hot Spot technology is that contact between bat and ball creates friction and in turn a localised increase in temperature, which appears as a bright spot in the infra-red image.

The advantage of Hot Spot over Snicko is, as opposed to the latter, Hot Spot clearly indicates the area that contacts the ball - the bright spot - whereas a sound and a spike on the Snicko graph could be anything between bat-ball, pad-ball or bat and pad.

The downside is that it is the most expensive technology in the DRS package, making its use in all matches practically difficult. Most cricket boards choose to not include Hot Spot in their DRS package due to this reason.

The Hot Spot will not be a part of the DRS package in use for the ongoing Test series between India and England because the required equipment could not be brought to India, by the time a late decision was made by the BCCI to trial DRS in this series.

Ultra Edge


The 'Ultra Edge' is Hawk Eye's upgraded version of the Snickometer for edge detection which was recently approved for use as part of the DRS package. Structurally, it is similar to the Snickometer which works with sound feed from the stump mic and visual evidence, however, Hawkeye’s improved, advanced version using live sound feed and its ultra-motion cameras is said to be more accurate in differentiating the sounds with more clarity

The 'Ultra Edge' system gained positive feedback from ICC representatives and India’s coach Anil Kumble, also the Chairman of ICC's Cricket Committee, when it was tested independently by engineers at the Massachusetts Institute of Technology (MIT) in Boston earlier this year and was introduced recently.

In the absence of Hot Spot Technology, the India-England Test series will be relying on the newly introduced Ultra-Edge technology to adjudicate leg-before, bat-pad and caught-behind appeals.


A look at the working of hawk-eye

The Hawk-eye is a multi-sport ball tracking technology invented by Dr Paul Hawkins and is used in sports such as tennis, football and cricket - among many others. In cricket, it is used to determine the predictive path of the ball with respect to the stumps, for making lbw decisions.

The hawk-eye, with the help of 6 cameras – three placed at each end of the ground - records the visuals of every delivery bowled, and the data obtained by the computers linked to the cameras is used to determine the predicted path of the delivery after pitching and impact on the pads.


When an appeal for lbw is made by the bowler and the on-field umpire refers it to the TV umpire, the visual representation of this predicted path guides the third umpire in passing his judgement.

Also read: DRS: What made BCCI give it a go ahead?

The point to be noted here is that, while constant attempts are being made to improve its efficiency by using higher frame rate ultra-motion cameras, the Hawkeye or any other ball tracking technology is still a work in progress, does not provide totally conclusive evidence and can only be used as a guiding tool that provides the umpire with predictive path of the ball for making a better judgement. Therefore, in the case of marginal decisions, the on-field decision will always be given priority.

The Day 1 of the ongoing 1st Test between India and England saw a similar call. In the 63rd over of the England innings, Joe Root was rapped on the pads by a full, in-swinging delivery from Umesh Yadav.

The original decision, communicated to the TV umpire by the on-field umpire Dharmasena, was Not Out, but ball tracking suggested it would just about clip the outside of leg stump. Being a marginal call, the umpire’s call stood and Root survived. While there will always be such occasional disputable calls, DRS helps in eliminating the very obvious umpiring howlers.

Published 10 Nov 2016, 19:38 IST
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