Sports Robot Officials: From Line Judges to ABB

Sports officiating used to be people in blazers sitting in chairs, staring at a line. Today most professional tennis matches are called by cameras, and Major League Baseball has just played its first regular season with a robot umpire on call. This post looks at the sports robot as an official: how line judges, umpires and ball kids ran a match, how Cyclops and Hawk-Eye took over the line calls, what went right and wrong this season, and where physical robots, including ABB arms and mobile robots, could fit at the side of the court.

The Hawk-Eye screen at Wimbledon shows a ball called in after a challenge, 2011. Photo: Mvkulkarni23 / Wikimedia Commons (CC BY-SA 3.0)

How umpires and line judges called the game

For most of the 20th century every call in tennis came from a person. A chair umpire ran the match from a raised seat at the net, line judges sat or stood at each line and shouted "out" or "fault," and ball kids ran the balls back to the players. The system depended on eyesight and nerve, and arguments were part of the show. At Wimbledon in 1981, John McEnroe shouted "you cannot be serious" at the umpire over a call, and later used the line as the title of his autobiography. Baseball worked the same way, with a home plate umpire judging every pitch by eye.

German player Fassbender argues with umpire Wellin at a tournament in Hilversum, 1975. Photo: Anefo / Nationaal Archief via Wikimedia Commons (CC0)

The first machine to take a call away from a person was Cyclops, introduced at Wimbledon in 1980. It sat a few millimetres above the court on the service line and projected six infrared beams. A serve that broke the beams beyond the line set off a beep for a fault. William Charles Carlton and Margaret Parnis England were named as inventors on the patent application, first filed in 1979. Cyclops only judged serves, and it had quirks: insects or dust sometimes broke the beams and caused "phantom beeps." Even so, it worked on the main courts for many years before cameras replaced it.

An umpire in his chair at the Dutch indoor tennis championships in Rotterdam, 1962. Photo: Harry Pot / Anefo, Nationaal Archief via Wikimedia Commons (CC0)

Those cameras came from Hawk-Eye, which Paul Hawkins and engineers at Roke Manor Research in Romsey, England, developed in 2000. It was first used in 2001 on television to analyse leg before wicket decisions in cricket. For tennis it uses ten high speed cameras, usually mounted under the stadium roof, and triangulates the ball's position frame by frame to rebuild its path in 3D. Tennis adopted Hawk-Eye for player challenges in 2006, and English football's Premier League used it for goal line decisions from the 2013 to 2014 season. Sony now owns the company.

A Hawk-Eye camera above the court at the Kremlin Cup in Moscow, 2012. Photo: JukoFF / Wikimedia Commons (CC BY-SA 3.0)

Electronic line calling and robot umpires this season

Hawk-Eye Live moved from replays to live calls at the 2017 Next Generation ATP Finals, where every line call was made automatically. The US Open used electronic line judges on most courts in 2020 to cut staff during COVID-19, and the 2021 Australian Open became the first Grand Slam to use them for every match. The ATP said in 2023 that all its tour events would switch by 2025, and Wimbledon dropped line judges in 2025. Roland Garros is the only Grand Slam that still uses them. Electronic calling is good, though not perfect. At this year's US Open, a malfunction ruled Anna Kalinskaya's forehand out on Court 5 when it had landed inside the line.

Line judges at the 2026 French Open, the last Grand Slam that still uses them. Photo: Like tears in rain / Wikimedia Commons (CC BY-SA 4.0)

The USTA admitted a system malfunction and said officials had also broken protocol, because the replay showed footage of a different point and no video review followed. The tournament added red lights on the net posts that flash when the system calls a ball out, after testing them at the United Cup and the Australian Open earlier in 2026. Baseball went further this year. The Automated Ball-Strike System, which uses Hawk-Eye cameras, was tested in the independent Atlantic League in 2019, then in the minor leagues. In MLB in 2026, human umpires still call pitches, but each team can challenge two calls per game and keeps a challenge when it wins.

Umpire Roberto Ortiz crouches behind home plate at a Tigers and Orioles game, 2017. Photo: Keith Allison / Wikimedia Commons (CC BY-SA 2.0)

The Associated Press reported on October 2, 2026, that the system overturned 54 percent of challenged calls in its first season. There were 10,557 challenges, about 4.35 per game, and catchers won 59 percent of theirs while batters won 49 percent. None of this is robotics in the sense of a moving arm. ABB does not make officiating systems, and no source shows its robots calling a match. Its arms have shown they can follow a fast ball, though: Google's GoalsEye table tennis project used an ABB IRB 120T arm, which we covered in our post on table tennis robots.

Students program an ABB IRB 120, the robot family Google used for its GoalsEye table tennis player. Photo: Peterantala / Wikimedia Commons (CC BY-SA 3.0)

Where court-side robots go next

What is left for people on court is mostly running and carrying. Ball kids still run and crouch at every point, and groundstaff mark the lines on grass and clay. On football fields, GPS guided robots from companies such as Turf Tank already paint the lines that officials will later judge. Nobody sells a robot ball kid for professional events yet. One would have to move fast, stay out of the players' way and never trip anyone. ABB's GoFa CRB 15000 is a cobot built to work next to people and stop when it senses contact, which is the kind of safety such a job would need.

A ball kid chases a ball across the court at the 2010 Australian Open. Photo: Sascha Wenninger / Wikimedia Commons (CC BY-SA 2.0)

Mobile robots would carry most of that work. ABB's Flexley Mover AMRs find their way through factories with Visual SLAM, and a smaller relative could in principle collect balls or carry towels and drinks along the back of a court, though ABB offers nothing like that today. A robot arm moving a ball along a known path might also be a way to check a camera system before a tournament, though we found no one doing that yet. Any such cell would be planned and tested first in RobotStudio, where reach and timing can be checked without a court.

The compact ABB Flexley Mover P603 carrying stacked crates. Photo: ABB

For homes and clubs, the open problems are cost and trust. A ten camera stadium system is far beyond what a local tennis club or a school baseball field can afford, so amateur players will mostly get cheaper camera and phone based tools first. Trust is harder. The Kalinskaya point shows that one wrong machine call, with no person ready to step in, does more damage than a missed call by a tired line judge, and players will keep asking who is responsible. Line judges are losing their jobs at most events, but chair umpires still handle the judgment calls, and baseball kept its plate umpires in charge.

ABB's GoFa cobot is guided by hand and stops when it senses contact. Photo: ABB

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