Third Umpire and DRS: How Technology Changed Cricket Decisions
The Decision Review System (DRS) and the third umpire together represent cricket's largest technological transformation since the introduction of helmets. DRS uses ball-tracking (Hawk-Eye), hotspot infrared cameras, and Snickometer audio to challenge on-field umpire decisions. This guide covers exactly how DRS works, what technology is used, which decisions can be challenged, and the most controversial DRS moments in cricket history.
DRS (Decision Review System) is the ICC's framework for using technology to challenge and correct umpiring decisions in international cricket. Each team receives a limited number of reviews per innings: in Test cricket, 3 unsuccessful reviews per innings per team; in ODIs and T20Is, 2 unsuccessful reviews per innings per team. A review is retained if the on-field decision is overturned (the technology supported the challenge); it is lost if the decision stands. Teams use reviews strategically — particularly to challenge LBW decisions and close caught-behind calls.
Hawk-Eye Ball Tracking
Hawk-Eye uses multiple high-speed cameras (typically 6-8 cameras positioned around the ground at different angles) to track the ball's trajectory from the moment it leaves the bowler's hand to impact. For LBW decisions, Hawk-Eye projects the ball's trajectory from the point of impact with the batsman's pad to where it would have continued — determining whether it would have hit the stumps. The projected trajectory carries a margin of uncertainty, displayed as a gradient zone: if more than 50% of the ball's projected path is within the stump zone, the decision is overturned (for umpire's call decisions where the ball is clipping the stumps). The umpire's call mechanism exists because Hawk-Eye's projection accuracy has a known error margin: predictions further from the point of impact (long-range projections) are less accurate than near-impact projections.
Edge Detection Technology
Caught-behind and caught-at-slip reviews require edge detection: Snickometer (developed in the 1990s) uses a microphone embedded near the stumps to capture the audio spike when the ball makes contact with the bat's edge — a sharp spike in the audio waveform indicates an edge. UltraEdge (more commonly used in modern DRS) combines the audio waveform with a high-speed video frame of the ball passing the bat — allowing reviewers to confirm that the audio spike coincides exactly with the moment the ball passes the edge. Hotspot uses infrared cameras to detect the heat trace left when the ball makes contact with bat or pad — friction between ball and surface creates a brief infrared signature that is visible even when the ball barely grazes the edge.
DRS in T20 Cricket
DRS in T20 cricket is more expensive to implement (all the technology must be deployed for a 3.5-hour match) and therefore less universally applied in T20 franchise leagues: the IPL uses DRS; the PSL uses partial technology. T20 DRS is less frequently used — most games are won or lost without a decisive DRS moment because the shorter innings reduces the number of close decisions that materially affect the result. Test cricket's longer format produces more DRS-critical moments, particularly in close Test matches where a single LBW decision in the last session can determine the winner (the 2019 Headingley Test — Ben Stokes 135* — included a crucial DRS moment where Australia's review was lost in the penultimate over).
Frequently asked questions
How does the DRS work in cricket?
DRS (Decision Review System) allows teams to challenge on-field umpire decisions using technology. When a team challenges an LBW decision, the review process uses Hawk-Eye ball tracking (projecting the ball's trajectory to determine whether it would have hit the stumps), UltraEdge or Snickometer (audio waveform detection of bat-ball contact), and Hotspot (infrared edge detection). For caught-behind appeals, UltraEdge and Hotspot are used. Each team has 3 unsuccessful reviews per innings in Tests (2 in ODIs/T20Is) — a review is retained if the decision is overturned, lost if the decision stands.
What is umpire's call in DRS?
Umpire's call is the DRS mechanism that preserves the on-field umpire's decision when the Hawk-Eye projection shows the ball hitting the edge of the stump (partially within the stump zone, partially outside). If the ball is clipping the edge — more than 50% of the ball's projected path within the stump zone — the umpire's call applies: if the umpire gave the batsman out, they remain out; if the umpire gave them not out, they remain not out. The umpire's call was introduced to acknowledge Hawk-Eye's inherent prediction uncertainty — the further the projection from the point of impact, the less certain the trajectory prediction. A ball clipping the edge of the stump is within the uncertainty margin.
When was DRS introduced in cricket?
DRS was introduced by the ICC on a trial basis in 2008 and became part of the official ICC playing conditions for Test cricket in 2011. It was extended to ODI cricket in 2011 and to T20 International cricket gradually thereafter. India's BCCI was the last major cricket board to accept DRS for home Test matches — they joined in 2016 after years of resistance (the India-Australia Tests without DRS in India drew significant criticism from observers, particularly when controversial LBW decisions affected results). Hotspot was originally part of the DRS package but is now optional — some series use it, others use only Hawk-Eye and UltraEdge.