Which calls are mine, and which belong to the players or line judges?

• Always yours: service foot faults, short serves and non-volley zone faults (Rule 19.A.1); service-motion faults and replays (Rule 20.E); other faults and replays; hinders; distractions; damaged balls; time-outs; and player conduct (Rule 17.D).
• No line judges: players call "out" for the baseline, sidelines and centerline on their own end of the court. You rule on those calls on appeal (Rule 19.B).
• With line judges: line judges call their assigned lines and foot faults and assist you as asked. Players call only the service centerline on their own end. Any other player line call is invalid, except to override an official's call in the opponent's favor (Rule 19.C).

During play you also confirm the correct server, receiver and positions, call the score, "point," "second server" and "side out," and keep the scoresheet (Rule 17.D).