How DRS Works: A Plain-English Guide to Cricket's Review System

A clear walkthrough of cricket's Decision Review System, from ball-tracking to the umpire's call, and why it still sparks debate.

Why cricket needed a review system

For most of cricket's history, the umpire's decision was final, full stop. That worked well enough when the game was slower and cameras weren't scrutinising every delivery in super slow motion.

But as broadcast technology improved, it became obvious that even excellent umpires got some close calls wrong, particularly on leg-before-wicket (LBW) appeals where a ball's future path has to be judged in real time. The Decision Review System, known almost universally as DRS, was introduced to correct the clearest mistakes without turning every decision into a lengthy inquiry.

The core idea is simple: each team gets a limited number of chances to ask for a second look at an on-field decision, using ball-tracking, sound, and image technology that the umpire doesn't have access to in the moment.

The tools inside DRS

DRS isn't one gadget, it's a bundle of technologies working together:

• Ball-tracking (commonly known by brand names like Hawk-Eye) predicts the path of the ball, including where it would have gone after hitting the pad, using cameras positioned around the ground.
• Ultra-Edge or Snickometer-style audio tools pick up faint sounds and match them against the moment the ball passes the bat, helping decide whether there was an edge.
• Infrared imaging (sometimes called Hot Spot) can show friction marks where the ball brushed the bat or pad, though it isn't used in every series.
• Replay footage from multiple angles helps with run-outs, stumpings, boundary calls, and catches close to the ground.

None of these tools acts alone. The third umpire, sitting in front of monitors away from the field, pulls together whichever pieces of evidence apply to the specific appeal and relays a recommendation to the on-field umpire.

How a review is actually called

A review can be initiated in two ways. Either the fielding side or the batting side can ask their on-field umpire for a review of a decision that has just been given, or an on-field umpire can refer a decision upstairs on their own, most often for run-outs, stumpings, or boundary catches where a naked-eye view simply isn't conclusive enough.

When a player wants to review, the captain or the batter facing the delivery signals for it, usually by drawing a rectangle in the air with their hands. There's typically a short time limit to make that call, so players have to decide quickly rather than waiting for a teammate's opinion from the dressing room. Once signalled, play pauses and the third umpire takes over.

Each team is allowed a small number of unsuccessful reviews per innings under current regulations, though the exact count can vary by competition and has changed over the years. Importantly, a review that is judged umpire's call, more on that below, doesn't count against a team's total in most formats, which softens the blow of a marginal request.

The umpire's call explained

This is the part that confuses newer fans the most. When ball-tracking shows that a delivery would have hit the stumps only marginally, by a small margin either in line, height, or width, the system defers to the original on-field decision rather than overturning it outright. This is called "umpire's call."

The logic behind it is that ball-tracking technology, however good, still involves some degree of predictive estimation for the part of the delivery after it strikes the pad. Rather than pretending that prediction is perfect down to the millimetre, the system builds in a margin of doubt and leans on the human umpire's original judgment when the outcome is genuinely borderline.

So if the on-field call was "out" and the tracking is close, it usually stays out; if the on-field call was "not out" and the tracking is close, it usually stays not out.

What DRS does and doesn't fix

DRS was designed to eliminate the clearest umpiring errors, the kind that used to change the outcome of a session or even a match, not to achieve perfect accuracy on every ball. It has been particularly effective for edges that were missed by the naked eye and for LBW shouts where the ball was clipping the stumps but looked like it might have been missing.

It has also changed the psychology of the game. Batters and captains now weigh probability rather than just gut feeling, since burning a review on a hopeless appeal leaves the side without one for a genuinely tight moment later in the innings.

A few practical things to know as a viewer

• DRS availability and the exact rules can differ between formats and tournaments, so it's worth checking before assuming the same limits apply everywhere.
• Not every ground or broadcast has access to every piece of technology, which is why some series rely more heavily on ball-tracking alone.
• Boundary and catch reviews tend to use pure replay rather than predictive tracking, since there's no need to estimate anything, the ball's position is either visible or it isn't.

Understanding these building blocks makes it much easier to follow the drama when a captain reviews a marginal call and the stadium holds its breath waiting for the big screen to reveal the verdict.

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