DRS Ball Tracking — How Hawk-Eye Works in Cricket Reviews

What Is Ball Tracking?

Ball tracking in cricket DRS (Decision Review System) uses a network of high-speed cameras positioned around the ground to reconstruct the ball's exact trajectory in three dimensions. The most widely used system is Hawk-Eye, developed by Paul Hawkins and first used in cricket in 2001. A competing system, Virtual Eye, is used in some series. Both reconstruct the ball's path and predict where it would have gone had the batter or their body not been in the way.

How the Cameras Work

Six to ten high-speed cameras (shooting at 340–600 frames per second) record the ball from multiple angles throughout its delivery. Frame-by-frame triangulation calculates the ball's exact position in 3D space at every moment. The system tracks the ball from the bowler's release, through the pitch, to the point of impact with the pad, and extrapolates the predicted path forward using physics models of ball deceleration, spin axis, and the pitch trajectory established from the pitch data.

The Trajectory Prediction

After the pitch point is established, Hawk-Eye must predict the ball's future path. The prediction accounts for: residual spin imparted at the point of impact, the ball's speed (which decreases after pitching), and the angle of the trajectory from the pitch point. For LBW reviews, the key questions are: (1) Did the ball pitch in line or on the off side? (2) Was the impact point in line with the stumps? (3) Would the ball have gone on to hit the stumps?

Umpire's Call Explained

When the ball tracking prediction shows the ball clipping the edge of the stumps within the ±2.5mm accuracy margin, the system returns 'Umpire's Call'. This means the technology cannot definitively say whether the ball would have hit or missed — the original on-field decision (whether out or not out) therefore stands. Umpire's Call means: if the umpire gave out, the batter remains out; if not out was given, they survive.