The US Open used Hawk-Eye for player challenges in 2006.
Hawk-Eye uses multiple high-speed cameras and computer vision to reconstruct a ball’s trajectory and estimate where it landed. Players could challenge line calls, with the system’s projected landing point used to review the umpire’s decision.
The 2006 US Open became the first Grand Slam tournament to use Hawk-Eye during play. At that event, each player received two incorrect challenges per set. The technology had already been used at tour events, including the 2006 Nasdaq-100 Open in Florida.
Hawk-Eye is often confused with VAR, which is primarily associated with football, or Cyclops, an earlier tennis device that focused on service-line calls. FoxTenn is a separate electronic review and line-calling system introduced later.