This is a Starcraft 2 strategy for Terran in dealing with rushes.
Terran is vulnerable to rushes because their earlier units are fragile. The way to flip this around is to wall your ramp.
Zerglings and Zealots are the most used units for early rushes. If you do not have a wall up, you are pretty much done. With a wall up and a few Marines behind the wall, defending against Zerglings and Zealots is easy.
The real strategy comes into play when defending the later rush. In order to defend the later rush, you need to know what your enemy's build is. This can only happen by scouting (or if your opponent tells you what he's building). For scouting, send out one of your SCV's. Another helpful way of knowing your opponent's move is using the Xel'naga Tower which reveals a large portion of the map. By knowing what your opponent is up to, you can have the right units to protect your wall and counter attack his build.
Here are a few examples of what works for counter building.
- What works well against Zealots are Marauders, Hellions, and Banshees.
- What works well against Sentries are Reapers, Hellions, Siege Tanks.
- What works against Roaches are Marauders, Siege Tanks, and Banshees.
- What works well against Marines are Reapers, Hellions, and Siege Tanks.
- Against Marauders, you want to use Marines or Banshees.
- Against Hydralisks, use Hellions.
Knowing what the enemy is going to attack with is important for a Terran player because Terran is not effective in fighting units that they are not prepared for.