What constitutes a successful serve in volleyball?

A successful serve in volleyball is one that lands in the opponent's court. This is the primary objective of serving — to deliver the ball in such a manner that it legally enters the opposing team's playing area, thereby putting them under pressure to receive and return the serve effectively. A successful serve can also be characterized by being difficult for the receiving team to handle, potentially leading to an ace, where the serve lands without anybody touching it.

When considering the other options, hitting the net does not count as a successful serve unless the ball goes over and lands in the correct area, which is not guaranteed. A serve that is caught by the opponent is considered a fault since players cannot catch or hold the ball — it must be hit cleanly. Lastly, a serve that is replayed indicates a disruption or error during the serve process, which does not fulfill the criteria for a successful send-off. Thus, the option that states the serve must land in the opponent's court accurately captures what defines a successful serve in the game of volleyball.