DRS Explained: How the Decision Review System Works in Cricket
The Decision Review System (DRS) lets teams challenge umpire calls. Learn how ball-tracking, UltraEdge, HotSpot, and review limits work in cricket.
The Decision Review System (DRS) was introduced in international cricket to reduce umpiring errors on dismissals. Teams can challenge an on-field umpire's decision using a combination of ball-tracking software, audio spike detection, and thermal imaging.
How DRS works
- A batsman is given out (or not out) by the on-field umpire.
- The fielding team (or batting team) believes the decision is wrong and signals a review within 15 seconds.
- The third umpire uses available technology to check the decision.
- The on-field call is overturned only if there is clear evidence the umpire was wrong.
- If the review fails, the team loses that review (but not if it was deemed 'umpire's call').
Review limits
| Format | Reviews per team | When reset |
|---|---|---|
| Tests | 3 | Each new innings |
| ODIs | 2 | Per innings (plus 1 extra after 35 overs) |
| T20Is | 1 | Per innings |
Technology components
Ball-tracking (Hawk-Eye)
Hawk-Eye uses six cameras around the ground to track the ball's trajectory. For LBW decisions, it predicts where the ball would have gone after hitting the pad. If the projection shows the ball hitting the stumps, the batsman is out — subject to 'umpire's call' if the ball is only clipping the stumps.
UltraEdge (Snickometer)
UltraEdge analyses the sound captured by microphones in or near the stumps. A spike in the audio waveform as the ball passes the bat edge indicates an edge. Combined with video frame matching, it confirms or denies thin edges that are invisible to the naked eye.
HotSpot
HotSpot uses infrared cameras to detect heat generated by friction when the ball contacts bat, pad, or body. A bright spot on the thermal image shows contact. HotSpot is not available in all matches due to its high cost.
Umpire's call
'Umpire's call' is applied when the ball-tracking shows the ball only partly hitting the stumps or hitting the edge of the bat impact zone — within a defined margin of uncertainty. In these cases, the on-field decision stands. If a team reviews and receives 'umpire's call,' they retain their review because the technology cannot definitively say the umpire was wrong.
What cannot be reviewed
- Wide balls and no-balls (except front-foot no-balls in some competitions)
- Running out of bowler's end on a stumping attempt
- Penalties and field placement decisions
- Boundaries (handled by the fourth umpire separately)
Frequently asked questions
How many DRS reviews does a team get in Test cricket?
Each team gets 3 reviews per innings in Test cricket. Reviews are reset at the start of each innings.
What is umpire's call in DRS?
Umpire's call means the ball-tracking or edge detection shows the decision is too close to call definitively. The on-field umpire's original decision stands, and the reviewing team keeps their review.
When was DRS introduced in cricket?
DRS was piloted in 2008 and gradually adopted. All major cricketing boards agreed to use it in home series by 2016.