DRS Ball Tracking — How Hawk-Eye, UltraEdge and Snicko Work

The Decision Review System (DRS) relies on a suite of technologies to review on-field umpiring decisions. The three core systems — Hawk-Eye ball tracking, UltraEdge (Snicko) sound detection, and ball-impact analysis — each address different aspects of a decision. Understanding how they work explains why some DRS outcomes feel counterintuitive.

Hawk-Eye Ball Tracking

Hawk-Eye uses six or more high-speed cameras positioned around the ground to triangulate the ball's three-dimensional position in every frame (filmed at 340 frames per second). From the observed trajectory, it constructs the ball's path from the bowler's hand to the pitch and beyond. For LBW reviews, Hawk-Eye predicts where the ball would have gone if the batter's pad had not intercepted it — using known ball physics (bounce angle, pace, spin rate) to project the trajectory. The system has a margin of error acknowledged by the ICC: the 'umpire's call' zone exists precisely because the boundary of whether a ball hits or misses the stumps carries genuine uncertainty.

Umpire's Call Zone

Hawk-Eye's predicted trajectory is accompanied by a 'confidence zone' — a range within which the ball's actual path could reasonably lie given measurement uncertainty. When the ball is predicted to be hitting the stumps but within this zone, the result is 'umpire's call' rather than a definitive 'hitting' — meaning the on-field decision stands. The zone is approximately 2.5 cm wide on either side of the stump edge. This is controversial because reviewers sometimes see 'hitting' displayed but the decision is 'umpire's call.'

UltraEdge (Snicko)

UltraEdge (branded as 'Snicko' by Channel 4 when first developed) uses a sensitive microphone embedded in the stump to detect sound spikes coinciding with the ball passing the bat edge. The audio waveform is displayed alongside slow-motion video — if a spike appears when the ball is level with the bat, it suggests an edge. The limitation: bat passing close to the pad also creates a sound spike. UltraEdge is decisive when the spike is large and unambiguous; contested when the spike is small or the ball simultaneously hits pad and bat.

Hot Spot (Infrared Imaging)

Hot Spot uses two infrared cameras to detect the heat signature left by friction when the ball strikes bat or pad. An edge leaves a heat mark on the bat face; a pad impact leaves one on the pad. Hot Spot is definitive for genuine edges — no heat mark, no edge. However, the technology is expensive, not universally deployed, and requires darkness in the image (clear backgrounds) to read heat marks accurately. Some boards do not include Hot Spot in their DRS deployment.