linesperson

A linesperson, also known as a line judge or line umpire, is an official in several sports responsible for observing boundary lines and determining whether a ball is in or out of play. They are part of the officiating crew and typically report to the chair umpire or referee during a match. The role is often performed by trained volunteers or paid professionals, depending on the level of competition.

In tennis, linespersons monitor the lines on the court—such as the baselines, sidelines, and service lines—and call balls as in or out. They use hand signals and communicate with the umpire, who has the final authority on calls. Modern tournaments may supplement linespeople with electronic review systems, such as Hawk-Eye, but human calls remain a core element of the officiating process.

In volleyball, line judges (often treated as synonymous with linespersons) focus on boundary lines and attack lines to determine whether balls land inside or outside the court. They position themselves along the sidelines and end lines and relay their calls to the referee and scorekeeper.

Beyond tennis and volleyball, similar boundary-call officials exist in other sports, with terminology varying by sport. Training emphasizes rule knowledge, proper signaling, positioning, and the ability to make rapid, accurate judgments under pressure. The use of technology is growing, but linespersons typically retain an essential role in communicating calls to players and audiences and in supporting fair competition.