DRS Technology in Cricket: How Hawkeye, Hotspot, and Snicko Work, and What 'Umpire's Call' Means
The Decision Review System (DRS) uses three technologies to review umpiring decisions: Hawkeye (ball-tracking, used for LBW reviews), Hotspot (thermal imaging, shows where the ball struck the bat or pad), and Ultra Edge / Snicko (audio waveform, detects edges). Reviews are initiated by players or captains. Each team gets 2 unsuccessful reviews per innings in Tests, 1 in ODIs. 'Umpire's Call' is the concept where the on-field decision stands if Hawkeye shows the ball hitting the wicket in the 'marginal zone.'
The Decision Review System (DRS) was introduced by the ICC in 2009 to review on-field umpiring decisions. It uses a suite of technologies to assess whether the umpire's decision was correct. Any player (or, in Tests, the batting or fielding team) can initiate a review — calling on the third umpire to check a decision. DRS has dramatically changed the game, reducing obvious errors but also introducing new controversies around technology limitations.
Hawkeye (Ball-Tracking)
Hawkeye uses 6–8 cameras positioned around the ground to track the ball's entire trajectory. For LBW reviews, it reconstructs: where the ball pitched (off stump, middle, leg — outside leg stump pitches cannot be LBW); where the ball hit the batsman (height above the stumps, position on the pad); and where the ball would have gone without hitting the batsman (would it have hit the stumps?). Accuracy: Hawkeye claims accuracy within 5mm. The Umpire's Call zone is applied when the ball would hit the bails or stumps within a 2.5-cm margin — in this zone, the on-field decision stands regardless of ball-tracking prediction.
Hotspot and Ultra-Edge
Hotspot uses thermal imaging cameras to detect heat generated by friction. When the ball touches the bat or pad, it leaves a heat signature (a bright white mark) on thermal imagery. Hotspot can detect thin edges that neither the on-field umpire nor Hawkeye can detect. Limitation: Hotspot requires expensive camera infrastructure and is not available at all Test venues. Ultra-Edge (Snicko) records the audio of each delivery on a high-sensitivity microphone and overlays it on the video frame-by-frame. A 'spike' in the audio waveform indicates the ball touched something (bat, pad, or ground) on that exact frame. Both technologies combined catch virtually all edges.
Frequently asked questions
Why did India resist DRS for so long, and what were the arguments for and against adoption?
India's DRS resistance: history, arguments, and eventual adoption. India was the last major Test nation to adopt DRS — they refused it from its 2009 introduction until 2016. The resistance came primarily from the BCCI (Board of Control for Cricket in India). Arguments India made against DRS adoption: (1) Technology unreliability: India argued that Hawkeye's predictive ball-tracking was not sufficiently accurate to overturn umpiring decisions. The BCCI president N. Srinivasan was quoted saying 'Why should we replace human judgment with computer simulation?' (2) Hotspot failure rates: Hotspot in early DRS iterations missed some genuine edges (cases where grease or sweat on the bat reduced the heat friction signature). India cited cases where DRS 'cleared' batters who clearly edged the ball. (3) Cost: DRS requires expensive camera installation (Hotspot cameras cost $500,000+). Developing nations and smaller venues struggled. (4) Political influence: some analysts argued India's resistance was partly driven by wanting 'home ground advantage' in LBW decisions — India's pitches and home umpiring historically benefited India's long batting partnerships. India's eventual adoption (2016): the ICC and other boards pushed India hard. By 2016, DRS technology had improved significantly — Hotspot was more reliable, Hawkeye accuracy was better documented. India's tour of England (2014) was played under DRS over Indian objections; the 2016 ICC test tour to India was the first in which India agreed to full DRS. Impact after adoption: DRS use in India eliminated several types of home-team bias that critics had alleged. India's LBW dismissal rates on home pitches increased slightly after DRS adoption — consistent with the hypothesis that some home LBW decisions had previously been favourable to the batting team.