It took an argument at a critical stage of the US Open in 2004 to make tennis realise that instant analysis by television would benefit players, spectators and even officials. Jennifer Capriati was playing Serena Williams in the quarter-finals of the US Open and received the benefit of four debatable calls in the final set, which she won 6-4. Within a year, the International Tennis Federation approved the Hawk-Eye ball-tracking system. Here is how technology has been used in other sports:

Rugby union The referee can call on a TV match official (TMO) to assist his decision-making if he has been unsighted. The TMO can rule, for instance, if a player grounded the ball or whether his foot was in touch before scoring a try. It has been criticised for the time taken to reach a decision, with some calling for a limit on the number of replays the TMO can use. Video referees are also used in rugby league.

American football Instant replay can be used to resolve a close call at the request of a team’s head coach, who throws a red flag on to the field to request a review. The referee has 60 seconds to study the play on a pitch-side TV and can overturn the call only if the evidence is incontrovertible. In the last two minutes of each half, the coaches may not challenge but a replay official, who sits in the stands, can if he spots an error.

Cricket From October — although there is a dispute about who will pay — players have been able to seek a review of a decision by appealing to a TV umpire. They are allowed three unsuccessful requests per innings, which must be made within a few seconds of the ball becoming dead. Only the batsman concerned or fielding captain may make the request.