The Decision Review System (DRS) is a technology-driven adjudication system used in international cricket to assist on-field umpires in reviewing contested decisions regarding dismissals (such as leg before wicket and catches) and boundary calls. Before the advent of DRS, contentious umpiring errors frequently altered the outcome of international matches without any mechanism for immediate correction. The International Cricket Council (ICC) first trialed the system in July 2008 during a Test match between India and Sri Lanka in Colombo, where Indian batter Virender Sehwag became the first international cricketer dismissed under player-initiated DRS. The system was officially incorporated into international match playing conditions in November 2009. The primary objective of DRS is not to re-adjudicate every close call, but to eliminate obvious, clear-cut human umpiring errors without destroying the on-field authority of the match officials.
DRS integrates three primary independent technologies synchronized by the TV Umpire (Third Umpire): ball-tracking trajectory software, acoustic edge detection, and infrared thermal imaging. For Leg Before Wicket (LBW) reviews, ball-tracking systems (predominantly Hawk-Eye or Virtual Eye) deploy synchronized high-speed cameras positioned around the stadium. The software tracks the ball's delivery, measures its speed, spin, and bounce, and calculates three mandatory physical parameters: pitching zone (where the ball pitched: in-line, outside off, or outside leg), impact point (where the ball first struck the batter's pad or person: in-line or outside off), and the projected path (whether the ball's mathematical trajectory would go on to hit or miss the stumps). For caught-behind and bat-pad decisions, the Third Umpire utilizes UltraEdge (or Real-Time Snickometer), which uses sensitive stump microphones to record ambient sound waves, displaying acoustic spike waveforms precisely synchronized with high-frame-rate video to differentiate bat contact from pad, glove, or ground friction. In addition, Hot Spot uses sensitive infrared cameras to detect micro-thermal heat signatures generated by friction when the ball strikes a wooden bat or batsman's pad.
A central, frequently debated operational principle of DRS is the "Umpire's Call" protocol. Because ball-tracking trajectory beyond the pad is a predictive mathematical extrapolation with an inherent margin of error, the ICC rules mandate that if the ball-tracking model indicates that less than 50% of the ball would strike the outer boundary of the stumps (or if the impact point is marginally in-line), the on-field umpire's original decision stands. When a review results in Umpire's Call, the reviewing team does not lose its allotted review quota. The ICC playing conditions grant each team two unsuccessful reviews per innings in T20 Internationals and One Day Internationals (ODIs), and three reviews per innings in Test cricket, governed by a strict 15-second countdown timer. For competitive examinations like UPSC, SSC CGL, and State PSCs, DRS questions appear under Sports, Applied Technology, and Current Affairs, testing the technologies behind Hawk-Eye, UltraEdge acoustic physics, infrared thermal dissipation, and the evolution of ICC match playing conditions.
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The Decision Review System (DRS) was officially introduced into international Test cricket by the ICC in November 2009 after initial trials in 2008.
The first international Test match to feature player reviews was played between India and Sri Lanka at the Sinhalese Sports Club in Colombo in July 2008.
Indian opening batter Virender Sehwag was the first player in international cricket history to be dismissed via a player review under DRS.
The primary stated purpose of DRS is to eliminate clear, obvious errors made by on-field umpires rather than re-umpire marginal decisions.
Teams have a strict 15-second countdown window after a ball becomes dead to signal a DRS review to the on-field umpire using a "T" sign.
Each team is permitted three unsuccessful reviews per innings in Test cricket and two unsuccessful reviews per innings in ODIs and T20 Internationals.
A reviewing team retains its review if the third umpire's final evaluation concludes as "Umpire's Call" on impact or hitting the stumps.
Hawk-Eye and Virtual Eye are the primary computer ball-tracking systems approved by the ICC to calculate predictive ball trajectories in LBW reviews.
Hawk-Eye uses a network of high-speed cameras (typically six or seven) calibrated around the cricket ground to track 3D coordinates of the ball.
In LBW reviews, ball-tracking evaluates three sequential criteria: Pitching (inside or outside lines), Impact (pad contact), and Wickets (hitting the stumps).
If a ball pitches outside the leg stump line in an LBW review, the batter cannot be given out under the laws of cricket, regardless of trajectory.
Umpire's Call on hitting the stumps applies when the predictive model projects that less than 50% of the ball would hit the outer edge of the stumps.
UltraEdge (Real-Time Snickometer) combines stump microphone audio frequency waveforms with synchronized high-frame-rate video cameras.
A sharp acoustic spike on the UltraEdge oscilloscope graph synchronized with the ball passing the bat indicates an edge or deflection.
Hot Spot uses two infrared cameras positioned at opposite ends of the ground to detect thermal heat generated by ball friction against bat or pad.
Hot Spot was developed by Australian inventor Warren Brennan using military-grade thermal imaging technology.
The Third Umpire first checks the bowler's front foot for a fair delivery (no-ball) before proceeding with the technological review steps.
The Marylebone Cricket Club (MCC) acts as the official custodian of the Laws of Cricket, while the ICC establishes DRS Playing Conditions.
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