The Decision Review System lets players challenge an on-field umpire’s decision. The batter, or the fielding captain, signals a T with their arms within 15 seconds of the decision, and the TV umpire takes a second look.
The technology
The TV umpire uses slow-motion replays, edge-detection tools that pick up the sound or heat of the ball touching the bat, and ball-tracking, which predicts where the ball would have gone after hitting the pad.
Umpire’s call
Ball-tracking has a margin of error, so when a prediction is very tight, for example the ball only just clipping the stumps, the original on-field decision stands. This is called umpire’s call. The reviewing team does not lose the review in that case.
Running out of reviews
Each team gets a limited number of unsuccessful reviews per innings. Once they are used up, the team has to live with every decision until the next innings, so captains try to save them for the clearest mistakes.
