A tennis ball touching the relevant line is in

Use a clear landing example

Imagine a fictional rally shot whose landing mark overlaps the singles sideline, with part of the mark beyond it. Because the ball touches the relevant line, it is in. The amount beyond the line does not turn partial line contact into an out ball.

Now imagine a mark with visible space between it and the outside edge of that sideline. That is a different landing relationship. A tight television angle may not show the gap clearly, so a still image can be less conclusive than a properly positioned line-calling system or official ruling.

The correct target changes with the shot

A serve must land in the correct service court, including its defining lines. A rally ball uses the applicable singles or doubles court boundaries. A ball in the doubles alley can be inside the doubles court during a rally but outside the service court on a serve.

Therefore, saying the ball touched a line is incomplete without identifying which line and what shot was being played. A baseline, service line and doubles sideline do not all define the same target area for every situation.

Keep player position separate from ball landing

Except for specific service and other rules, a player can stand outside the court to return a ball that remains in play. A receiver moving into the alley does not by itself prove the serve landed outside the service box. Watch the ball’s actual landing.

Also distinguish a ball that looks headed out from one that has landed out. A player volleying it before the bounce has played a live ball; its projected landing is not an already completed out call.

For a replay note, record singles or doubles, serve or rally, the relevant boundary and the official call. This sequence explains why a ball partly over a line can be good while another ball landing inside a wider court area can still be a service fault. The rule depends on the applicable target and actual contact, rather than a general impression that the shot was close.

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