Early rushes can come in a few forms and fashions, but they're all based on the same tactic – to distract and set you back as much as possible before you have the chance to build any army or even build a decent economy. Rushes like this typically are entry level tier 1 units, such as zealots, marines or zerglings. Sometimes SCV's, probes and drones may also join in the attack to make the rush a little more effective.
Fighting early game rushes can be frustrating, especially if you aren't prepared to deal with it. However, early rushes can grant you a significant advantage in terms of economy and tech, as these rushes are usually of the 'all in' type or semi all-in type, where your opponent throws as much as he has against you, in the hope that you are set back significantly or quit. Here are some common rushes, how to deal with them and general advice on fighting it off:
This is your major defense against ANY early rush. Signs such as 2 or more rax/gateway or early spawning pool are dead giveaways. Other rushes can also be spotted with an early scout, such as canon rushes, bunker rushes, spine crawler rushes and planetary fortress rushes. Proxy rushes can also be easily spotted if you scout early.
No gas usually indicates an early rush. Most early rushes are mineral heavy, and the rushing player will typically not get gas, as they want to mine as much minerals to rush early, and back up the rush with typically the same unit type.
No pylons or barracks in your opponents base usually means there's one near your base, and you need to scout around your base very quickly to catch the rush before your opponent sets up shop in your base. Check all the dark areas in your base and areas nearby your natural or surroundings. Protoss players typically like to proxy a pylon near some of the nearby mineral fields, so be sure to scout there as well. Generally, a scout will reveal an early rush and almost completely nullify its effects.
Zergling rush/early zealots
If you're playing on a small map, or have been scouted early by a zerg player (eg. 3/6 o clock spawning positions) you can almost certainly expect an early rush. If you're playing a 2v2, 3v3 or 4v4 and there's a zerg opponent, a rush is almost inevitable, as the zerg player will try to buy some time for his allies to get their plans in order while you and your allies are busy trying to deal with his zerglings.
A wall off can put a quick stop to this. Build supply depots, barracks engineering bay or any combo of the above to prevent the zerglings from getting in. This will stop the zerglings from getting in and hurting your economy. Don't forget to pull some SCV's off the line to repair your damaged buildings! If you right click on 'repair' you can set them to auto-repair, which means that not only will they repair the buildings, but themselves as well! Especially helpful if you're doing a 2v2, 3v3 or 4v4 and a marine gets sent in to help the rush. Move your damaged SCV to the back, and get him repaired, and keep the SCV's with full health at the front. Zealots are a little tougher, but nothing a wall that's being repaired with some SCV's can't handle!
Part 2 Coming Soon!
This strategy brought to you by Zan
Zan is an old Starcraft/Brood War player who recently made the switch to Starcraft 2. He is making lots of mistakes but learning quickly from them as he goes along. You can learn about most of his blunders and close calls at Starcraft2TerranStrategies.com. He can be seen trying to fight under the name "klesk" on battlenet, so feel free to take advantage of his general n00bishness if you see him there – you'll get a chance to read about what he's learned from it here!