Much like musicians, snipers, in the series, are an optional and alternative occupation for any Marine or pirate. Snipers usually have great eyesight and accuracy, allowing them to hit difficult targets from a considerable distance. Due to their choice of weaponry, snipers excel best at long-range combat. Weapons that most snipers prefer to utilize include rifles and pistols, but can also include artillery such as cannons and mortars and highly customized weapons that best suits the sniper's skill.
Snipers with great physical strength can throw seemingly harmless objects without any launchers, turning them into deadly projectiles of tremendous accuracy and precision. Fish-Men are the most prominent of such feats, turning water droplets into high-velocity bullets, especially those who practice Fish-Man Karate.
As the term sniper is often associated with firearms (as well as terrorism, especially following the 2002 Beltway snipings) in the United States, the 4Kids-dubbed anime always translates it as marksman or sharpshooter. The Viz manga and the Funimation anime use sniper more freely, but on occasion have been known to use these substitutes as well.
Given the nature of their skills, some snipers - such as Usopp - may double as the crew gunner, responsible for operating and maintaining the ship's cannons and artillery.
While not considered traditional snipers (due to the lack of weaponry), both Trebol and Charlotte Katakuri were shown to precisely hit targets from long distances with ease.
↑One Piece Manga and Anime — Vol. 20Chapter 183 (p. 15) and Episode 113, Sanji demands Usopp's goggles back from Mr. 2. The Viz manga has him refer to Usopp as the crew's "sniper", while the Funimation anime uses "sharpshooter".