An Underhand Serve or an Underhand Service is a controversial but legal tennis technique where players deliver the ball from below shoulder level.
This rarely-used serve is often viewed negatively by the tennis community, despite being within the rules. Players typically employ it as a tactical surprise, when dealing with injuries, or when experiencing shoulder pain.
While some consider it unsportsmanlike, others argue it's a legitimate strategic option, particularly against opponents who position themselves far behind the baseline.