DRS and Ball Tracking Explained: Reviews, Umpire’s Call and Technology
How the Decision Review System works in cricket, including ball tracking, UltraEdge and umpire’s call, and how teams use reviews to challenge decisions.
The Decision Review System, almost always called DRS, lets teams challenge an on-field umpire’s decision and have it checked with technology. It was designed to reduce clear mistakes, not to replace the umpire. It is used in Tests, one-day internationals and Twenty20 internationals where the host board agrees, and in many domestic leagues. This guide explains how it works and why the on-field call can sometimes stand even when the replay seems to disagree.
How a review works
When a batter is given out, or not out, the batter or the fielding captain can ask for a review within a short time limit, normally 15 seconds. The on-field umpire refers the decision to the third umpire, who has access to the technology and replays. The third umpire examines the evidence and tells the on-field umpire if the decision should change. A team whose review fails normally uses up one of its limited number of reviews, while a team that succeeds keeps it. The number of reviews each side has is set by the competition and varies by format, so it is best to check the playing conditions.
The technology behind DRS
DRS combines several tools. Each answers a different question:
- Ball tracking uses a set of high-speed cameras to follow a delivery and predict where it would have gone. It is mostly used for leg before wicket decisions.
- Edge detection tools identify whether the ball touched the bat. These are sound-based systems, known by names such as Snicko and UltraEdge, which pair audio with video. In earlier years, a thermal imaging system called HotSpot was also used.
- Slow-motion and high-resolution replays help assess catches, run-outs and stumpings.
For an lbw decision, the third umpire follows a set order. First, did the ball pitch in line or on the off side? Second, was the point of impact in line with the stumps? Third, would the ball have gone on to hit the stumps? The ball-tracking system provides a prediction for the final step.
What is umpire’s call?
Ball tracking is a prediction, not a certainty, and has a margin of error. To allow for that, the system uses the idea of umpire’s call. If the tracking shows the ball clipping the stumps by only a small amount, within the margin of error, the decision stays the same as the one the on-field umpire made. If the umpire had given the batter out, the batter stays out. If the umpire had said not out, the batter stays not out. How umpire’s call affects a team’s remaining reviews is set out in the playing conditions.
The same applies to the point of impact in some cases. If the ball hits the batter only slightly in line with the stumps, it may also be treated as umpire’s call. For that reason, a replay showing the ball clipping the stumps can still result in a not-out verdict.
Where DRS has limits
DRS is not used everywhere. Cost and availability of the equipment mean that many lower-level matches do not have it. Even at the highest level, the technology can sometimes give inconclusive evidence, and the on-field decision then stands. For example, if there is no clear evidence that the ball touched the bat or the glove, the original decision is kept.
There is also debate about how closely the technology reflects reality. Ball tracking relies on a model of the ball’s flight, particularly after it pitches, and some critics say the predictions are imperfect. Supporters argue that DRS has made decision-making fairer and removed many obvious errors.
How teams use reviews
A review is a limited resource, so teams use it carefully. The batter and the non-striker often talk about an lbw appeal, because a batter knows whether they hit the ball. Bowlers and wicketkeepers lean on one another and the captain makes the final call. A well-timed review can swing a match, particularly when it removes a set batter. A poor one can leave a team without a safety net late in an innings.
In summary, DRS combines ball tracking, edge detection and replays to help the third umpire check a decision. Umpire’s call is the safety margin that keeps the original decision in close cases.
Frequently asked questions
What does umpire’s call mean?
It means the technology shows the ball only marginally hitting or missing the stumps, so the on-field umpire’s original decision stays as it was.
How long do players have to ask for a review?
In international cricket the time limit is generally 15 seconds from the moment the decision is given.
How does ball tracking work?
Several high-speed cameras follow the ball, and software uses that data to predict the path it would have taken after hitting the batter. It is mainly used for lbw decisions.