What counts as a fault
A fault immediately ends the rally, and the most common causes are: hitting the ball out of bounds or into the net, volleying while touching the kitchen (see kitchen positioning), volleying before the two-bounce rule is satisfied, and an illegal or out-of-box serve (see legal serve 2026). Any of these results in a fault against the player or team that committed it.
The line rule: in or out
A ball is considered in if any part of it touches any part of the line — it doesn't need to land fully inside the line. This surprises players coming from sports with different line rules. A ball that clips the outside edge of a line is still in play.
Who makes the call in recreational play
Without officials, the general convention is that each side calls faults on balls landing on their own side of the court, since they have the best view of exactly where it landed. Calling a ball out on the opponent's side, where your view is worse, is generally discouraged.
Handling disputed calls fairly
Close calls happen. The common etiquette is that if you're genuinely unsure whether a ball was in or out, you give the benefit of the doubt to your opponent and play it as in. This keeps the game fair and avoids disputes that slow down casual and social play.
