Measurement in sport – the long and the short of it
Box 5 | Using technology for line-ball calls
Sports such as cricket and tennis continue to get faster with innovations in the materials used for balls, bats and racquets. Similarly, video recording technology has improved over the past few decades, leading to better quality images for viewers. The problem is that clearer images show that umpires make mistakes.
In 1992, video replays were first used in cricket to help determine if a player was out. If an umpire wasn’t quite sure of a decision, he could refer it to the third umpire. (There are two umpires on the field during a cricket match.) By viewing the moment in slow motion, it was easier to tell if a player was run out, or if a ball had carried to a fielder for a catch. Video referees have also been used in rugby league since 1998 to make decisions about tries.
However, even a video system has its flaws. Sometimes on a run-out call in cricket, the stumps are broken between frames in the recording and you can’t tell if the bat has crossed the stumps in time. Even when this doesn’t occur, there is still a degree of human error in the decision—two people viewing the same replay might disagree on the outcome. Some people believe this human element is a part of the game and should be maintained. Others feel that the higher the accuracy the better.
A system has been developed by Hawk-Eye Innovations that removes the subjectivity of video replays. It is used in tennis, cricket and snooker, with a system for soccer being developed. Several cameras are set up around the playing area. They are carefully calibrated so that a three-dimensional position of the ball can be established. The path of the ball is tracked through the air, creating a three-dimensional representation. Hawk-Eye was first introduced to cricket in 2001. It is used to judge leg before wicket calls, as it can predict what the path of the ball would have been if it had not been interrupted by the batsman. It was first used in tennis in 2006, where it is used to indicate whether the ball bounced in or not. As well as being used to adjudicate, Hawk-Eye is a useful statistical tool as it records the flight of each ball for comparisons. Questions have been raised about the accuracy of Hawk-Eye, despite claims from the manufacturer. As with any such system, it is unlikely to be correct 100 per cent of the time. However, as technology improves, the accuracy will also improve.
Boxes
Box 1. Olympic track and pool facilities
Box 2. Perfect timing: Timing devices and reaction time
Box 3. Physics in sport: Forces on an athlete
Box 4. Rackets and balls
Related site
Energy basics (Nova: Science in the news, Australian Academy of Science)
Posted February 2012.