This purpose of this guide is to give players an idea of the mindset and execution (in a general sense) of early aggression. Many games are decided by the way that players handle early aggression. Having a good understanding of early aggression is therefore very important to success in Starcraft 2.
Acts of early aggression can be broken up into four flavors: Cheesing, Rushing, Harassing, and Pressuring. Each requires a specific mindset along with correct execution to be effective.
Cheese
Cheese refers to builds that, if unscouted, can be very devastating. However, if the cheese fails to do damage, typically the cheesing player is left in an extremely bad position. Fairly often, cheese is an "All In" attack. The most defining feature of cheese is typically speed. Cheeses are designed to hit early and hard, generally getting attacking units to the enemy base around the 3 minute mark. This speed comes at the expense of your economy. Cheeses will leave you with many fewer harvesters than you otherwise would have in a standard game, and it is therefore important to make up this disadvantage by doing hefty damage to the opponent.
What differentiates cheese from the other forms of early aggression is that defending it will require a large deviation from your standard build order to be able to defend. The classic example of cheese is the 6 pool. Defending this opening as Terran and Protoss requires a very different opening build order than you would otherwise use. It also represents a different opening than you would like to do going into the midgame. For example, defending a 6 pool as Protoss typically involves creating an airtight wall, which must be later broken down in order to attack or expand. In addition, your cyber core is often delayed.
As a cheesing player, you must be prepared to realize that a proper defense will normally result in you being too far behind to effectively compete in the game. Therefore, if you are cheesing, commit to the attack. Don’t be afraid to bring along two SCV's to build one bunker, since losing a lone SCV will delay your attack timing far too long. This doesn’t mean you shouldn’t think about a game plan for after the cheese, and indeed some people try to gain a macro lead with cheese openings. Jermstuddog posted a build he entitled the "Fail Pool" (http://www.teamliquid.net/forum/viewmessage.php?topic_id=160550 ) which is a macro focused 8-pool opening.
As the defender, you should not be afraid to do things that you would otherwise not do (like walling in as Protoss). The key as the defender is to realize that surviving without suffering irreparable damage will generally leave you ahead. The mindset you must have is essentially, "All I need to do is survive." Do not be afraid to pull some probes (or SCV's/drones) to hold off the cheese.
Rush
A rush is a potent early attack, done with the intent of dealing major damage to the opponent. Rush build orders focus on getting a number of units out early, sacrificing either in slower tech or with a later expansion. These disadvantages can be made up by either delaying your opponents expansion, killing his workers, or killing structures. Unlike pressure, a rush is not effective if only other units are killed, unless you can follow up on the initial rush and do some more tangible damage.
A rush differs from cheese in a few ways. First, a rush needs to do far less damage to be effective. The attack also occurs much later, typically from 5-8 minutes in. Most importantly, defending a rush should require a much more subtle change in your standard opening. In particular, your opening build order should be designed specifically to be safe (assuming some scouting) to most rushes with only minor adjustments. Rushes are best used to counter an opponent that has expanded early, or is teching hard.
The execution of a rush is very similar to that of cheese. A rushing player needs to commit to the rush, and focus his attention on controlling and reinforcing his army. In order to be effective, a rush build order must be sharp. If you decide to use a rush, it should be done early in the game, as many as two to three minutes before you plan on attacking. You need to be aggressive and do some damage, but since you have not sacrificed as much as a cheesing player, it is important to not overcommit. Losing your army before doing major damage or expanding will result in a loss. If you are able to do some damage, like forcing a cancel on an expansion, do not be afraid to forgo the rush and transition into a more macro game style while using your army to pressure the opponent.
As a defender, it is important to identify if your opponent is rushing you, or is just pressuring you. A rushing player will act much more aggressively than a pressuring player. A defender can use this aggression against the opponent. Force the player to engage you in a choke, or in a similar position with favorable ground. Keep up with your macro and heavy unit production, but do not neglect your economy and continue to tech. This is in contrast to defending against cheese, where often you need to completely stop teching and boosting your economy (at least for a moment) to be able to defend. Rushing players have large armys, and you will need a large army to hold him off. Also understand that the way rushes beat you is that they rattle you. Rushes get an imposing army in your face early, and can cause you to make mistakes in your macro and control. If you can, the plan you are using to hold off a rush should leave you feeling comfortable. An example could be force fielding your ramp while waiting for colossus against a 3-rax push. Do not be too over eager to engage the opponent, and rather focus on your army and production, making the opponent come to you.
Harass
Harass is similar to a rush, in that it sacrifices something early on to attack the opponent. However, where rushes are normally designed to defeat the enemy army, harass uses high tech units to circumvent the army, and is generally targeted at the economy of the opponent. Because of this, harass will almost never actually kill someone. Its purpose is to slow or hamper your opponent and make him play defensive. Because you force the opponent onto the defensive, a harassing player normally will expand or tech while they harass.
Harass is very different from the other forms of early aggression. It generally relies on fast, mobile units in small numbers. In addition, harass requires a well thought out follow-up plan to be effective. Since harassment rarely ever kills or even deals a heavy blow to an opponent, it is important to have some other wrinkle in the game plan in order to win the game. Switching over to a rush can work, since your harass has slowed his economy and forced certain tech paths. More commonly, harass is used to occupy an opponent while you expand and tech, and thus ends up close to pressure in the players mindset.
Execution of harass can be difficult. It requires very good micro (relative to your opponents skill) to be effective. All the time spent microing means that it can be difficult to simultaneously macro. Harassment is also very fragile, in the sense that a moments indecision, or one wrong decision can mean the end of the harass. If this occurs too early, the harassing player is left in a poor position to defend any counterattack. It is therefore critical to keep your harassing units alive, both to continue delaying your opponent and so that your army is stronger against a counterattack. However, harassment can be effective even if it does only a little damage. In terms of mindset, harass is very close to pressure, even though their execution is very different.
As the defender, you cannot overcommit to defending against the harassment. If you see a lone banshee coming in, do not overreact by laying down a forge and cannons all over. It is best to learn how to defend harass by using units you would want against a midgame army, like stalkers against banshees rather than trying to tech to phoenix. Respond by producing extra workers in case you do lose some harvesters. The control of a defender is also important against harass, since defending against harass often requires you to divide your forces to defend multiple locations. It is also important to peer into the harassing players greater game plan. It is very important to identify if he will try and rush you off his harass, or switch to a macro game. Fortunately, this is fairly easy to scout simply by checking his natural expansion.
Pressure
The final style of early aggression is pressure. In pro games, most early aggression is designed to be pressure. It is a very diverse style of agression, with several different forms. The goal of pressure is to delay or hamper your opponent. This can be done either with a contain, probing attacks, or a delayed or weakened rush. Pressure retains the ability to deal major damage to your opponent if he has cut too many corners early, however can also get a very early expansion.
Pressure is different from other early aggression in that it doesn't have to kill anything to be effective. A properly designed pressure opening can be very effective if it can force the opponent to do certain things and or delay an expansion. For example, take a 2-rax pressure opening against protoss. The terran player can expand while the force moves out. The attacking force is also large enough and potent enough to force the opponent to stay defensive for a while, securing an economic lead as the game moves on.
While presure and rushes look very similar in gameplay, they require vastly different mindsets and builds. Pressure will often forgo a production structure to get up an earlier expansion, while a rush maximizes the potency of the initial force. In addition, a rushing player needs to have an aggressive mindset, and needs to do some real damage to avoid falling behind. A pressuring player must focus on showing an aggressive posture, but also must protect his pressuring force at all costs. A pressuring player should abandon his aggression at the first signs of difficulty, since your force is likely not strong enough to hold up in a full engagement. Remember that pressure only needs to hamper an opponent, not kill him.
Defending pressure requires a very different mindset than that against other early agression. In a way, the defender must switch over to an aggressive mindset, and try to break the pressure as early as possible. Because this is so different from how a rush is defended, identifying whether an attack is a rush of pressure is very important. Scouting is the best way do to this, in particular scouting how many unit production structures he is using, or when/if he has taken his natural expansion. However, you can also look at the way the attacking player behaves with his army to see what kind of aggression it is. A pressuring player must be far more timid with his force than a rushing player will. He is more likely to sit at the bottom of your ramp and wait rather than try and force his way up.
