DRS Technology Explained: Hawk-Eye, UltraEdge, Hot Spot and How They Work
The technology behind cricket's Decision Review System — how Hawk-Eye ball tracking works, what UltraEdge does for caught-behind decisions, and why some technologies are more accurate than others.
The Decision Review System (DRS) uses multiple technology systems to assist umpires in making correct decisions. The core technologies are: Hawk-Eye (ball tracking for LBW decisions), UltraEdge (audio spike detection for caught-behind and LBW reviews), Hot Spot (thermal imaging for bat contact), and ball-tracking cameras. Each technology has specific applications, specific limitations, and specific controversies. Understanding how each works helps viewers interpret DRS reviews accurately.
Hawk-Eye Ball Tracking
Hawk-Eye uses six or more cameras positioned around the ground to track the ball's trajectory in three dimensions. For LBW reviews, Hawk-Eye extrapolates the ball's path after the point of impact with the pad, predicting where it would have gone had the pad not been there. The extrapolated path determines: whether the ball pitched in line (outside leg = not out), whether it hit the pad in line, and whether the projected path would hit the stumps. The final part — the projection — introduces a margin of uncertainty, resulting in 'Umpire's Call' when the ball clips the stump edge.
- UltraEdge: Microphone arrays embedded in the stumps capture audio — a spike (sudden increase in sound) at the moment the ball passes the bat indicates contact. UltraEdge can detect thin edges too fine to see on normal cameras. Limitation: it also detects bat-pad contact (ball hitting pad against bat) that looks like a bat-edge.
- Hot Spot: Thermal imaging cameras detect friction heat — a white mark on a dark thermal screen shows where the ball made contact. Hot Spot is the most definitive technology for bat contact. Limitation: very thin edges produce almost no heat; Hot Spot misses these.
- Snicko: An older version of audio spike detection; replaced by UltraEdge. Still used in some cricket boards.
- Ball-tracking cameras: Fixed high-speed cameras track the ball at 1000+ fps for stump-camera, snickometer, and general pitch-of-the-ball calls.
Frequently asked questions
How does Hawk-Eye work in cricket?
Hawk-Eye in cricket uses six or more cameras positioned around the stadium to track the ball's three-dimensional trajectory from release to impact. For LBW reviews, it calculates three things: (1) where the ball pitched — in line, outside off, or outside leg; (2) where the ball impacted the pad — in line or outside the stumps; (3) where the ball would have gone had the pad not been there — the projected path. If the projected path would have hit the stumps, the batter is out; if it would have missed, the batter is not out; if it clips the edge of the stumps (within the error margin), 'Umpire's Call' is applied and the on-field decision stands.
What is UltraEdge in cricket?
UltraEdge is a sound-detection technology used in cricket's DRS to identify whether a ball made contact with the bat or bat handle. Sensitive microphones capture audio throughout the delivery; when the ball passes the bat, any contact creates a sound spike (sudden amplitude increase) on the audio trace. The third umpire reviews the UltraEdge trace alongside video replay to determine if a spike coincides with the ball passing the edge of the bat. UltraEdge can detect extremely thin edges that create no visible deflection; its limitation is that it also picks up bat-pad sounds that can be confused for bat-edge contact.
What is Hot Spot in cricket?
Hot Spot is a thermal imaging technology used in cricket's DRS to detect bat contact. Two high-speed infrared cameras (one positioned on each side of the pitch) capture thermal images of the bat, ball, and body. When the ball makes contact with the bat, friction creates heat — a white spot on the thermal image. Third umpires check for a white mark on the bat face corresponding to the moment the ball passed. Hot Spot is considered the most definitive bat-contact technology; its limitation is that very thin edges produce almost no heat signature and may not show on the thermal image.