The umpire in tennis oversees the match to ensure the rules are followed.
They call the scores, make decisions on disputed points, and can overrule line calls.
There are also line judges who help the umpire by watching the lines to see if the ball lands in or out.
In major tournaments, instant replay systems like Hawk-Eye are used to review close calls.
The umpire’s job is to keep the game fair and orderly.