Umpire Decision Review System
The Umpire Decision Review System (UDRS or DRS) is a technology-based system used in cricket to assist the match officials with their decision-making. On-field umpires may choose to consult with the third umpire (known as an Umpire Review), and players may request that the third umpire consider a decision of the on-field umpires (known as a Player Review).
The main elements that have been used are television replays, technology that tracks the path of the ball and predicts what it would have done, microphones to detect small sounds made as the ball hits bat or pad, and infra-red imaging to detect temperature changes as the ball hits bat or pad.
While on-field Test match umpires have been able to refer some decisions to a third umpire since November 1992, the formal DRS system to add Player Reviews was first used in a Test match in 2008, first used in an ODI in January 2011, and first used in a Twenty20 International in October 2017.
DRS was preceded by a system to allow on-field umpires to refer some decisions to the Third umpire to be decided using TV replays, in place since since November 1992.
The addition of Player Reviews and additional technology to this system was first introduced in Test cricket, for the sole purpose of reviewing controversial decisions made by the on-field umpires as to whether or not a batsman/batswoman had been dismissed. The system is based on the concept of player - referral conceived by Senaka Weeraratna (Sri Lankan lawyer). He was the first to suggest a Player Referral System for Cricket in a letter published in the ‘Australian’ national newspaper on March 25, 1997. Until he drew public attention to the benefit of such a player referral system there was no such system or mechanism even in other Sports, prior to March 25, 1997. The Player Referral system was first tested in an India v Sri Lanka match in 2008, and was officially launched by the ICC on 24 November 2009 during the first Test match between New Zealand and Pakistan at the University Oval in Dunedin. It was first used in One Day Internationals (ODI) in January 2011, during England's tour of Australia. The ICC initially made the UDRS mandatory in all international matches, but later made its use optional, so that the system would only be used if both teams agree. The ICC has agreed to continue to work on the technology and will try to incorporate its use into all ICC events.
In October 2012, the ICC made amendments on lbw protocols, increasing the margin of uncertainty when the ball hits the batsman's pad. In July 2016, the rules were amended once again, reducing the margin of uncertainty. The updated rules were first used in the ODI match between Ireland and South Africa in September 2016.
In September 2013, the ICC announced that for a trial period starting in October 2013, a team's referrals would be reset to two after 80 overs in an innings in Test matches. Previously each team had a maximum of two unsuccessful reviews in an innings.
Starting in November 2014 from Australia's ODI series versus South Africa, the field umpires' communications have also been broadcast to the viewers. Whenever a decision is reviewed by the TV umpire, the umpire's communication with the field umpire and the reply incharge can be heard.
In February 2017, the ICC agreed the use for all future ICC World Twenty20 tournaments, with one review per team. The first T20 tournament scheduled to use the technology will be the 2018 ICC Women's World Twenty20. It was used in Knockout stages of Pakistan Super League 2017, which was the first time DRS used in a T20 league. DRS was used for the first time in Twenty20 International in India-Australia T20I series in October 2017.
Under the new ICC rules as of November 2017, there would no longer be a top-up of reviews after 80 overs in Test matches, and teams will have only 2 unsuccessful reviews every innings. However, teams would no longer lose a review for an umpire's call on an LBW review.
The components in UDRS are:
- Television replays, including slow motion.
- Hawk-Eye, Eagle Eye, or Virtual Eye: ball-tracking technology that plots the trajectory of a bowling delivery that has been interrupted by the batsman/batswoman, often by the pad, and can predict whether it would have hit the stumps.
- Snickometer or Ultra-edge (Hawk-Eye's version): directional microphones to detect small sounds made as the ball hits the bat or pad. The use of the original Snickometer was superseded by Real Time Snicko in 2013.
- Hot Spot: Infra-red imaging system that shows where the ball has been in contact with bat or pad. Improved cameras were introduced for the 2012 season. The system came under fire after the 2013 Ashes in England. It was claimed that using silicone tape prevented faint edges being picked by Hot Spot, which was later confirmed by a MIT report.
- Run out. If the on-field umpires are unable to decide if the batsman is out, they may request the third umpire to ascertain whether the batsman had made it home. Also the case where both batsmen have run to the same end and the on-field umpires are uncertain over which batsman made his ground first. An example of this was the Third Test between New Zealand and the West Indies in 2006.
- Stumped, bowled and hit wicket, in which cases the Third Umpire first checks the delivery was not a no-ball.
- Caught and Obstructing the field if both umpires are unsure. In some cases the fielder may catch the ball a few inches above ground level. If the umpire's vision is obscured or is unsure if the ball bounced before the fielder caught the ball, he can refer the decision. For these dismissals, the on-field umpire must give a “soft-signal” to say whether or not they think it is out and the third umpire must find conclusive evidence that the on-field decision is incorrect. For Caught, the Third Umpire first checks whether the delivery was a no-ball and whether the batsman hit the ball.
- Whether the delivery causing any dismissal was a no-ball.
Note the on-field umpires may not request the Third Umpire review an LBW decision (apart from whether the delivery was a no-ball).
The on-field umpires may also request the Third Umpire reviews the following:
- Boundary calls (to see if a batsman/batswoman hit a four or a six). In some cases the ball may bounce just a foot inside the boundary rope resulting in four runs. If the umpire needs to ascertain if it had been a 4 or a 6, he may consult the third umpire. Near the boundary, often a fielder may dive to save the ball from travelling beyond the boundary. If the fielder makes any simultaneous contact with the boundary and the cricket ball, 6 runs are declared. A third umpire may also be consulted in such a case.
- Whether the ball has hit cameras on or over the field of play.
Umpire Reviews are also available to the on-field umpires when there is a Third umpire but the full UDRS is not in use. In this case, the Third umpire uses television replays (only) to come to a decision, and not the additional technology such as ball-tracking.
A fielding team may use the system to dispute a "not out" decision and a batting team may use it to dispute an "out" decision. The fielding team captain or the batsman/batswoman being dismissed invokes the challenge by signalling a "T" with the arms or arm and bat. A challenge is only used in situations that did or could result in a dismissal: for example, to determine if the ball is a legal catch (making contact with the batsman/batswoman's bat or glove and not touching the ground before being held by a fielder), or if a delivery made the criteria for an LBW dismissal.
Once the challenge is invoked, acknowledged, and agreed, the Third Umpire reviews the play.
Each team can initiate referrals until they reach the limit of unsuccessful reviews. This limit is two unsuccessful review requests per innings during a Test match, and one unsuccessful review request per innings during a One Day International. From 2013 until September 2017, the number of reviews available for a team in a Test innings was topped-up to two after 80 overs. From October 2017, if the on-field decision remains unchanged because the DRS shows "umpire's call", the team will not lose its review.
The third umpire then looks at various TV replays from different angles, comes to a conclusion, and then reports to the on-field umpire whether his analysis supports the original call, contradicts the call, or is inconclusive. The on-field umpire then makes the final decision: either re-signalling a call that is standing or revoking a call that is being reversed and then making the corrected signal. Only clearly incorrect decisions are reversed; if the Third Umpire's analysis is within established margins of error or is otherwise inconclusive, the on-field umpire's original call stands.
Originally decisions were conveyed in traffic light style (a red light indicating a batsman's dismissal, a green light not out); it is now common practice to display the decision via the large screen scoreboard, if available. If the umpire is unsure if a batsman is out or not, due to lack of conclusive evidence, the usual procedure is to acquit the batsman, known in cricketing parlance as "the benefit of the doubt".
The instant replays are also available to the TV/Internet viewers.
Officiating replay system
In 2013, ICC tested a broadcaster-free replay system. Under the experiment, a non-match umpire sits in a separate room with a giant monitor and has discretion over which replays to see rather than relying on the broadcaster. The non-match umpire mirrors the role of the third umpire without having the duty of making adjudications. The system was first used in an Ashes Test (where Nigel Llong performed the duties of non-match umpire) and was repeated in a Pakistan-Sri Lanka ODI.
After the Stuart Broad incident, in The Ashes 2013, ICC has started to take steps to give third umpire access to instant replays. This is regardless of calls being referred to by on-field umpires. By doing so, ICC wants to make sure that any obvious mistakes are avoided in future.
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The Decision Review System has generally received positive response from players and coaches since its launch, however there have been some criticisms as well. West Indies legend Joel Garner labelled the system a "gimmick". Another West Indian Ramnaresh Sarwan said that he was not a supporter of the experimental referral system. Former umpire Dickie Bird also criticised the system, saying it undermines the authority of on-field umpires. The cricketing board of India has expressed a sceptical view on the adoption of the system if it is near perfect. Pakistani spinner Saeed Ajmal expressed dissatisfaction over the Decision Review System after a semi-final of the 2011 Cricket World Cup against India. He said that DRS showed the line of the ball deviating more than it actually did. Hawk-Eye officials admitted in December 2014 that their review technology made an error in a decision to give Pakistan opener Shan Masood out in the second Test against New Zealand in Dubai (17-21 November 2014). At a meeting held at the ICC office in Dubai two weeks later, Hawk-Eye is understood to have conceded to Pakistan captain Misbah-ul-Haq and team manager Moin Khan that the projection used by their technology for the Leg before wicket decision was incorrect. Also, a challenge can only be made by the captain within a 15-second window from when an initial decision is made, but it can be lengthened if no clear decision is made, especially they are assumed not out if there is no reaction by the umpire. In 2019 Virat Kohli labelled DRS inconsistent. 
Player Review statistics
- 26% of Player Reviews resulted in on-field decisions being overturned.
- Reviews by batsmen were less frequent than reviews by bowling teams, as 41% of reviews were by batsmen and 59% by bowling teams.
- Reviews by batsmen were more likely to be successful, with a 34% success rate, compared to a success rate of about 20% for bowling teams.
- 74% of referrals were for LBW, 18% for wicketkeeper catches, and the rest for catches elsewhere or indeterminate reason. The success rate was only 22% for LBW, compared to 40% for wicketkeeper catches.
- There were on average about 1.4 batting overturns and 1.2 bowling overturns per match. Initial fears that DRS would bring an increase in the number of dismissals have, therefore, not come true.
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Appendix D, paragraph 1.1.6, THIRD UMPIRE (NON-DRS), Replays that can be used: The third umpire shall only have access to replays of any camera images. Other technology which may be in use by the broadcaster for broadcast purposes (for example, ball-tracking technology, sound-based edge detection technology, and heat-based edge detection technology) shall not be used during Umpire Reviews.
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