Sniping
From Liquipedia StarCraft Brood War Wiki
Sniping refers to a player killing a valuable enemy unit (or rarely a building) without directly engaging the opponent's army. This is most commonly done against spellcasters or heavy support units, as these units are the most crucial in direct battles. Although this can be done with melee units, it is most easily done with fast ranged units.
Competitive Use[edit]
Zerg[edit]
Generally, Zerg players have the most to gain from sniping important units. Both Terran and Protoss rely on spellcasters to damage the Zerg's army, so killing these units before they engage is very powerful. Against Protoss, High Templars, Reavers, Observers, and Archons will often be the Zerg's primary target when they are present in small numbers. Against Terran, Zerg focus on eliminating as many Science Vessels from the battlefield as possible, by the use of Scourge, Mutalisks, or a combination of a Defiler's plague spell and an attacking unit such as a Mutalisk or Hydralisk.
Terran[edit]
While Terrans often do not have as many opportunities or the necessity to snipe units the way a Zerg player does, it still can be accomplished. The most common unit for sniping when playing in a Terran vs. Protoss match-up is the Vulture, specifically after the speed upgrade has been researched. Vultures can quickly and effectively dispose of High Templars, Dark Templars, Zealots, and Archons that are currently in the process of transforming.
In Terran vs. Zerg, there is a constant play between the Science Vessels sniping units with irradiate, most Lurkers, Mutalisks, Ultralisks, and Defilers, and avoiding Zerg units attempting to snipe those same Vessels at the same time.
In Terran vs. Terran, almost the only match-up that sees large numbers of Battlecruisers on a regular basis, their Yamato Cannon ability is used. Most frequently it utilized to snipe the front line of your opponent's Tanks, so you can push your Tanks further forward.
Protoss[edit]
Because they rely more on spellcasters and heavy support units, sniping is most useful for a Protoss in PvP. Dragoons are fairly fast and have good range, so they are usually the best suited units. The Dark Archon's Feedback spell is also effective at sniping spellcasters due to its long range.