DRS Explained — How the Decision Review System Works in Cricket

The Decision Review System — universally known as DRS — is the suite of technology-assisted tools that allows players to challenge the on-field umpire's decisions in international cricket. Introduced by the ICC in 2008 and made mandatory for all ICC-sanctioned matches in 2016, DRS has changed the game by dramatically reducing the number of howlers and rewarding smart, well-timed reviews.

How many DRS reviews does each team get?

A review is retained (not lost) if it is successful — the original decision is overturned. A review is lost if it fails. Teams therefore guard their reviews carefully, especially late in a T20 innings when one review is all they have.

What technology does DRS use?

• Ball-tracking (Hawk-Eye / Virtual Eye): uses multiple cameras to reconstruct the ball's trajectory and predict whether it would have hit the stumps. Used for LBW reviews — specifically the pitching, impact, and hitting-the-stumps checks.
• Ultra-Edge (Snickometer): analyses audio from stump microphones in real time to detect whether there was an edge. A spike on the audio waveform at the moment the ball passes the bat indicates contact — used for caught-behind and caught-at-slip decisions.
• Hot Spot: infrared cameras that detect friction heat left on the bat or pad when the ball makes contact. Hot Spot is used as supplementary evidence alongside Ultra-Edge; most broadcast packages rely on Ultra-Edge as the primary edge-detection tool.
• Real-Time Snickometer (RTS): an improved version of the original Snickometer that syncs audio waveforms to video frames in real time, allowing the third umpire to compare exactly when the sound occurs relative to bat and ball.

What is 'umpire's call'?

Umpire's call is the most misunderstood part of DRS. It applies to LBW reviews involving ball-tracking. The ball-tracking system predicts a probabilistic range — not a single line — of where the ball will go. When only part of the predicted zone clips the stumps (the impact or the hitting-the-stumps check), the ICC introduced the concept of umpire's call to acknowledge that the technology is not precise enough to definitively overrule the on-field decision in a marginal case.

The three LBW checks in a DRS review

1. Pitching: did the ball pitch in line? If the ball pitched outside leg stump, the batter cannot be out LBW regardless of where it was going — the review immediately fails this check.
2. Impact: did the ball hit the batter in line with the stumps? If impact was outside off stump, the batter can only be out if they were not playing a shot (pad-play). If the impact is marginal, umpire's call may apply.
3. Hitting the stumps: ball-tracking projects the ball forward and checks whether it would have hit the stumps. If more than half the ball is hitting at least half the stump, it is out. If only part of the projected zone clips the stumps, umpire's call applies.

When can a team take a DRS review?

Only the batting or fielding side affected by an on-field decision can request a review — and only within 15 seconds of the umpire signalling the decision. The fielding captain or the batter at the crease must signal to the umpire by drawing a rectangle in the air with their index fingers (mimicking a TV screen). The umpire then refers the decision to the third umpire, who reviews the available technology and communicates the conclusion.

Decisions not covered by DRS

DRS cannot review: no-balls (except beamers and front-foot no-balls, which were added as optional checks in 2020), wide calls, and run-outs/stumpings in some tournaments where only Hot Spot and ball-tracking are available. It also cannot review a decision the umpire did not make — for example, a fielder cannot review a not-out verdict simply because they believe the batter was run out if the umpire did not call it out in the first place, unless the bowling team uses their review to request the check.