A chair umpire in tennis is the main umpire who sits right beside the court on the sideline. Their primary responsibilities are to call out the score and any final rulings, while making sure all of the rules of tennis are being followed.
A chair umpire is one of four umpires present at a tennis match. Their position is known as "chair umpire" because they sit in a tall chair during the match. The chair is located just off the center of the court on the sideline, even with where the net is. This location is ideal because it gives the umpire a great view of the court, all of the lines, and both players. The chair umpire is the head umpire out of the four.
According to the USTA Chair Umpire Handbook, during a match "Everything!" is the chair umpire's responsibility. Chair umpires are in charge of the match and everything that happens in it. One main responsibility of a chair umpire is to announce the score of the match after every point, game, and set. Line umpires call if a ball is in or out of bounds, but the other rulings during a match are up to the chair umpire. They deal with players arguments, they make decisions on if a match should be delayed for weather, and they enforce every rule on the players. If a player needs to be called for a warning or a violation, it is up to the chair umpire to make the call.
Chair umpires also have many responsibilities before and after the match. Before the match they are in charge of making sure the court and net are set up to regulation for the specific match, ensuring that there are enough tennis balls for the match, and conducting a pre-match meeting with the players that includes a coin toss to decide who serves first.
After a match, chair umpires are responsible for announcing the final score, double checking their scorecard, and turning in the scorecard and game balls to the referee.