DRS Explained: How Ball-Tracking, UltraEdge and HotSpot Work in Cricket's Decision Review System
A complete guide to the Decision Review System (DRS) in cricket — ball-tracking technology (Hawk-Eye), UltraEdge audio analysis, HotSpot thermal imaging, how reviews are used, and what 'umpire's call' means.
The Decision Review System (DRS) allows players to challenge on-field umpiring decisions by referring them to the third umpire, who reviews available technology to either uphold or overturn the decision. DRS was introduced in international cricket in 2008 and is now used in most Test matches and major limited-overs tournaments. Each team gets a limited number of reviews per innings (2 in Tests, 1 in ODIs and T20Is), which they lose if the review upholds the on-field decision and they retain if the review successfully overturns it. DRS consists of multiple technological components working together: ball-tracking (Hawk-Eye), edge detection (UltraEdge/Snicko), and thermal imaging (HotSpot).
Ball-Tracking (Hawk-Eye): LBW Predictions
Hawk-Eye is the ball-tracking technology used to determine the predicted path of the ball after it hits the batsman's pad — essential for LBW reviews. Six cameras (or more) around the ground capture the ball's trajectory from the bowler's hand to the point of impact on the pad. A computer models the ball's continued path based on its trajectory, speed, and expected behaviour, predicting whether it would have hit the stumps. The technology considers: the ball's trajectory before impact, seam position, any lateral movement, and the angle of trajectory. The predicted path is shown as a coloured cone (wider further from the stumps to show increasing uncertainty at longer distances). For an LBW decision, the review checks: (1) Was there an inside edge? (UltraEdge), (2) Did the ball pitch in line? (Hawk-Eye), (3) Would it have hit the stumps? (Hawk-Eye).
UltraEdge (Snicko): Detecting Edges
UltraEdge (also known as Ultra-Edge or Snickometer) is audio-visual technology that detects whether the ball has made contact with the bat or batting glove. It works by: synchronising a high-frequency microphone (or multiple microphones) with a frame-by-frame visual display of the ball passing the bat edge. If there is a spike in the audio waveform precisely as the ball passes the bat, it suggests edge contact. The technology is used for: caught behind decisions (did the ball touch the bat before reaching the wicketkeeper?), LBW decisions (was there an inside edge before hitting the pad?), and caught in the infield decisions where ball-bat contact is unclear. UltraEdge has largely replaced the original Snicko technology, which used a similar principle but was less synchronised.
HotSpot: Thermal Imaging for Contact Detection
HotSpot uses infrared (thermal) imaging cameras to detect the heat generated when ball meets bat (or pad or glove). Friction from contact creates a heat mark visible in thermal imaging, even if the contact is barely perceptible in regular video. HotSpot is particularly effective for thin edges — glances off the outside of the bat — where UltraEdge audio might be ambiguous. However, HotSpot has limitations: it requires good camera angle coverage, cannot detect all types of contact (a ball brushing through pad gauze or hitting helmet without friction may leave no mark), and is not available in all venues. As a result, HotSpot is supplementary to UltraEdge rather than a replacement — third umpires use both technologies together when reviewing edge decisions.
How the Review Process Works Step by Step
- On-field umpire makes a decision (Out or Not Out)
- The dismissed batsman or fielding captain indicates they want to review (T-shape gesture with arms)
- Review must be requested before the next delivery is bowled
- Third umpire reviews all available technology for the specific decision type
- For LBW: checks edge (UltraEdge), pitch point (Hawk-Eye), impact point (Hawk-Eye), and projected path (Hawk-Eye)
- For caught behind: checks UltraEdge audio spike and HotSpot thermal mark
- Third umpire communicates result: 'Wicket stands', 'Wicket overturned', or 'Umpire's call'
- If overturned: the team retains their review; if upheld (including umpire's call): review is lost
Frequently asked questions
How many DRS reviews does each team get in cricket?
In Test cricket, each team gets 2 unsuccessful DRS reviews per innings. In ODIs and T20 internationals, each team gets 1 unsuccessful review per innings. A review is only 'used up' (lost) if the on-field decision is upheld by the third umpire — if the review successfully overturns the decision, the team retains it. 'Umpire's call' reviews (where the on-field decision stands due to technology uncertainty) count as unsuccessful reviews and the team loses them.
What is Hawk-Eye in cricket DRS?
Hawk-Eye is the ball-tracking technology used in DRS to predict the path of a cricket ball after it hits a batsman's pad — essential for LBW reviews. Multiple cameras track the ball from delivery to impact, and a computer models the predicted path based on trajectory, speed, and seam position. The prediction shows whether the ball would have hit the stumps. Hawk-Eye also determines whether the ball pitched in line with the stumps — a prerequisite for an LBW decision when the batsman is struck outside the off-stump line playing a shot.
What does 'umpire's call' mean in cricket DRS?
Umpire's call applies when Hawk-Eye or another technology shows the decision is within the uncertainty margin of the technology — the ball was so close to the edge of the stump, or the contact was so marginal, that the technology cannot definitively determine the correct outcome. When umpire's call applies, the on-field decision stands regardless of whether it favoured batsman or bowler. The team that called the review loses it (the review counts as unsuccessful). Umpire's call exists to acknowledge the limits of technology and preserve the authority of on-field umpires for genuinely marginal decisions.