How do line calls work?

Each team calls "out" for all lines on its own end of the court; in doubles, either partner can call (Rule 8.A).

• A ball touching any line is in, except a serve that lands on the kitchen line, which is out (Rules 8.B, 8.C).
• Only call "out" if you clearly see space between the ball and the line (Rule 8.E). A ball you can't promptly call out is in, and the opponent gets the benefit of the doubt (Rule 8.D).
• Call "out" promptly by voice, hand signal, or both. If you return the ball, your call must come before the opponent hits it or the ball becomes dead; otherwise play continues (Rule 8.F.3).
• Shouting "out" or "bounce it" to your partner while the ball is still in the air is communication, not a line call (Rule 8.F.4).
• If partners disagree, the ball is in (Rule 8.H).
• You may ask your opponent's opinion until the next serve. If they make a clear call, it stands (Rule 8.I).
• Spectators must not be consulted on any call (Rule 8.J).