Tennis - line umpires and chair umpires

In the sport of tennis, there are two types of on-court officials, or judges. These are the chair umpire and the line umpires. While their jobs have similarities, they are very separate.     

The chair umpire is equivalent to a home base umpire in baseball in that he has the final say and is in charge of the others in his crew. His judgment reigns supreme over anyone else's on the court. The rule book calls the chair umpire "the final authority on all questions of fact during the match." What this means is that this person has the last word on:            

-whether or not a ball was in;
-calling of service lets and foot faults;
-any line umpire calls where the chair umpire is certain a mistake has been made.

Thus, the chair umpire supersedes anything a line umpire says when appropriate. They are also responsible for ensuring that match pace is in keeping with the rules and for completing the scorecards which are the official records for any game played.

One final ability that the chair umpire has is to hand out penalties throughout the match for improper behavior. We've all seen this. There have been some very notable tennis greats with big mouths and attitudes, and when those mouths and attitudes get too big, the chair umpire doles out immediate punishments. Penalties can be imparted for any of the following:

-profanity;
-delay of game;
-equipment abuse (racket and/or ball);
-verbal or physical of players and/or umpires;
-any other unsportsmanlike conduct.

In contrast to all of the above 'powers', the line umpires have a much more confined duty with much less power. The number of line umpires can vary in a match, but beforehand, each line umpire is given their assignment. This could be a single line or a combination of playing area. They communicate with a combination of verbal calls and hand signals. Simplified, their responsibility is to call a ball safe or out. When their line of sight is obstructed by a player or other object, the chair umpire makes the decision.

The other obvious difference between the chair umpire and the line umpires is that the chair umpire is seated in a tall chair in the middle of the court. This throne-like spot gives them a look at the entire court. The various line judges, however, are down on the court itself, by their assigned line. If they are assigned multiple lines, the line umpires actually move to those different court areas as dictated by match play.

In short, the chair umpire is the big boss, able to overrule anyone else on the court and to affect the match by assessing penalties when necessary, while the line judges have a more limiting role in a finite part of the court.