When is a serve deemed legal?

A serve is deemed legal when it adheres to the established rules of re-serving. These rules specify conditions such as the server's positioning, the manner in which the ball is contacted, and the trajectory of the serve. For instance, the server must stand behind the end line and must strike the ball within a specific timeframe and manner. Additionally, the serve must reach the opposing team's side of the court without violating any other game rules, such as touching the net, being executed after the official signal, or any other infractions that could render it illegal.

While a serve must cross the net to be valid and can be executed either overhand or underhand, the key factor is compliance with the overarching rules governing serves. Therefore, the accuracy of a serve being considered legal lies in its conformity to these re-serving rules rather than merely its physical execution or successful crossing of the net.