DRS, or the Decision Review System, helps cricket officials revisit close dismissal decisions using video, sound analysis and ball-tracking technology. Hawk-Eye is mainly used to reconstruct a ball’s path for LBW reviews, while UltraEdge helps identify a possible contact between ball and bat. Neither system replaces the umpire: they provide evidence to the third umpire, who decides whether that evidence clearly supports overturning the original on-field call.
What DRS is designed to do
According to the ICC, the Decision Review System is a technology-based process that assists match officials with decision-making. It has two broad routes. An on-field umpire can consult the third umpire through an Umpire Review, while players can request a Player Review of an on-field decision concerning a dismissal.
The system developed from the use of television replays by third umpires, which had been available for certain decisions since 1992. Formal player reviews arrived later: DRS was first used in a Test match in 2008. Over time, the system has become a familiar part of international cricket broadcasts, particularly during LBW appeals, fine edges, close catches, run-outs and stumpings.
A review begins with an on-field decision, not with technology searching for a new one. A batting side can challenge an out decision, while the fielding captain can challenge a not-out decision. The third umpire then examines the relevant evidence, including replays and, where available, specialist DRS tools. The essential standard is whether the evidence identifies a clear error in the original call.
The main technologies behind a review
DRS is not a single machine or a single camera feed. It is a collection of tools that answer different questions. Slow-motion video can establish whether a batter made their ground or whether a catch carried cleanly. UltraEdge can assist with the question of contact. Ball tracking can assist with the likely future path of a delivery stopped by the batter’s pad.
This distinction matters because each technology has limits. A sound spike does not by itself explain what made the sound, and a projected ball path is not the same as footage of an event that has already occurred. The third umpire considers the available evidence in context rather than treating any one display as an automatic verdict.
For viewers assessing a team’s options before a match, Cricket Match Prediction can sit alongside an understanding of how reviews may influence key moments, especially when close LBW or caught-behind decisions arise.
Video replays and camera angles
Television replays remain the starting point for many third-umpire decisions. Different camera angles, slow motion and frame-by-frame viewing can help establish events that occur too quickly for the naked eye. Run-outs and stumpings, for example, often depend on whether the batter’s bat or body was grounded behind the crease when the wicket was put down.
Replays are also important for catches. The third umpire may need to judge whether the ball touched the ground before being held, whether it was a bump ball, or whether a fielder’s contact with the boundary turned a save into a four. In dismissal reviews, the delivery’s legality can also be relevant, including whether a no-ball must be called.
How Hawk-Eye ball tracking works
Hawk-Eye is the best-known ball-tracking element of DRS. Its role is to plot the observed part of a delivery’s trajectory and then predict what would probably have happened had the ball not been interrupted, usually by the batter’s pad. In an LBW review, that projection helps the officials examine whether the ball would have gone on to hit the stumps.
The ball-tracking process breaks an LBW assessment into separate stages. The technology can show where the ball pitched, where it struck the batter, and the projected path towards the wickets. These are commonly presented on screen as “pitching”, “impact” and “wickets”. The third umpire must still apply the Laws and the DRS protocol to those findings.
The comparison published in the Decision Review System overview lists Hawk-Eye with six cameras operating at 340 frames per second. Multiple camera viewpoints help create a more detailed reconstruction of the ball’s movement than a single broadcast angle could provide. However, the displayed flight after impact remains a calculated prediction based on the delivery’s measured path.
Why projected paths are not treated as absolute
Cricket uses the principle of “umpire’s call” for marginal LBW findings. This preserves the original decision when ball tracking does not show a sufficiently clear reason to reverse it. The approach recognises that a very close projection should not automatically override an on-field umpire who had to make a real-time judgement.
Umpire’s call can apply when the estimated impact is marginally in line with the stumps or when the projected path marginally clips the wickets. It is not used to decide where the ball pitched or whether the batter hit the ball first. When umpire’s call applies, the on-field decision stands, but the reviewing side does not lose its review.
This outcome can be confusing because the broadcast graphic may appear to show the ball clipping the stumps. The key question is not simply whether a graphic shows contact with the wicket. It is whether the relevant part of the projected ball is sufficiently within the defined decision area to demonstrate that the original decision was clearly wrong.
How UltraEdge detects a possible edge
UltraEdge, also called Real Time Snicko or RTS, is used to help identify faint contact between ball and bat or pad. The system uses directional microphones to detect small sounds around the moment the ball passes the batter. Its display presents an audio waveform, where a spike may indicate a relevant noise.
The timing is crucial. The third umpire checks whether the spike occurs immediately before, during or immediately after the ball passes the bat. The sound trace is assessed alongside the video, rather than in isolation. A ball striking the pad, bat hitting the ground, or another nearby sound can create noise, so synchronised images and audio are central to the interpretation.
UltraEdge is especially useful in caught-behind appeals, where a thin outside edge may be too slight to be obvious from standard replays. It can also matter in LBW reviews, since confirmed bat contact before pad impact can change the basis of the decision. Its purpose is to improve the evidence available to the third umpire, not to decide whether a batter is out on its own.
Hot Spot and other supporting evidence
Some DRS arrangements have also used Hot Spot, an infra-red imaging system that can show a mark where the ball has contacted a bat or pad. The Decision Review System overview describes it as an additional component, though its availability has varied. Technologies can differ across matches because the equipment and competition protocols are not always identical.
This is why commentators often specify which tools are available before or during a series. A review conducted with video replays and UltraEdge may not have the same evidence set as one that also includes ball tracking or infra-red imaging. The ICC notes that full third-umpire protocols appear in the playing conditions for each competition.
What happens after a player signals for a review
A player review is usually signalled by making a “T” shape with the arms, or with an arm and bat. The request must concern a dismissal decision. The third umpire reviews the incident independently, communicating the result to the on-field umpire after checking the relevant points of fact.
For an LBW decision, the analysis may include whether the delivery was legal, whether the batter hit the ball, where the ball pitched, where it struck the pad and its projected path. For a caught decision, the sequence may include possible bat contact, the fairness of the delivery and whether the catch was completed cleanly.
The final on-field outcome can be “out”, “not out”, “umpire’s call” or an unchanged decision because the evidence is inconclusive. The visible review process may feel lengthy, but it reflects the need to examine a sequence of separate questions rather than relying on one replay or graphic.
Technology supports judgement, rather than replacing it
DRS has made close decisions more transparent by showing viewers much of the evidence considered by officials. It can correct clear errors that would have been difficult to resolve using eyesight alone, particularly in fast-paced incidents. At the same time, it deliberately retains a role for the original umpire’s judgement when the evidence is too marginal.
Hawk-Eye, UltraEdge and replay technology work best when understood as complementary tools. Ball tracking addresses projected movement, sound analysis addresses possible contact, and video provides visual context. Together, they give the third umpire a stronger basis for a decision while preserving the principle that only clear errors should be reversed.
