Zergling RushZergling rush is an effective micro strategy because it allows the player to get into the opponent's base early in the game, that is unless it has been walled in. Protoss players will have more trouble defending against a zergling rush than another Zerg or Terran.
The Zerg race has the fastest rush in the game. In the right hands, a zergling rush strategy can be skillfully executed to break into a Protoss base early on in the game. Breaking into a Terran base with a Zergling rush is nearly impossible when you are matched against a skilled player capable of building a proper Terran wall on the ramp leading to his base.
Protoss, however, usually have a hole in the wall because they don’t have structures that allow them to fly or lower into the ground like Terran. Once a Protoss structure is built it will remain in that place until it is destroyed and there is nothing you can do about it!
Because of this, the creativity of Protoss players has produced a new tactic that helps in replacing non-movable buildings. This is done by simply placing units in the way of other units, effectively blocking opponent’s forces.
By the way, unit-blocking is one of the tactics that belongs to the category of unit control based strategies. Unit-blocking is also discussed on this website in greater detail as one of the completely legitimate unit control tactic using which the player can greatly increase the chances of winning more Starcraft games.
Placing one of the units inside the opening of a Protoss wall will disallow zerglings from getting in, however, without a Photon Cannon at the ramp entrance to the base belonging to a Protoss player, a skilled Zerg player can still outsmart that configuration and break in early to chop up a decent number of probes, significantly slowing down the Protoss player.
Yes, it’s possible to block the entrance hole with a first-tier unit such as a Zealot, but remember that the Zealot unit has to use the "Stop" command. This means that the Zealot will not react to the incoming zerglings. A seemingly harmless bit of knowledge that can help us exploit the situation.
This is great news for the zerglings, because now the Protoss has the choice to either watch his wall being attacked (which will cause at least some anxiety) or move his Zealot unit and risk having his base open for the entire swarm of zerglings to get in, which, in the hands of a skilled zerg player they should be intentioned to do.
Zealot’s Stop command and idleness allows the Zerg player to attack the nearby buildings that are part of the wall, without the Zealot doing anything about it. Once the Protoss player sees that, they will "Un-stop" the Zealot. This fatal mistake can be used to the advantage of the Zerg player. Using this very moment, direct your entire zerglings army to enter his main base through the opening and eradicate his drones.
Skilled Protoss players would not allow for this situation to happen. They would build a Photon Cannon which in combination with the idle "hole guardian" Protoss is at least one of the proper solutions for killing off zergling rushes as Protoss. One blast from a Photon Cannon deals enough damage to kill one zergling. A skilled Protoss player can also focus on building a Stalker unit sooner to block the entrance and use the ranged attack ability to fight off the zerglings.