A Shift In Focus
Besides Ultra Combos, Focus Attacks are the biggest new feature of the Street Fighter IV series. Focus Attacks are an interesting system, as they act almost as a "multi-tool" in the Street Fighter world. They can be used for defensive purposes, absorbing hits like a Parry. They can be used as an offensive aid, allowing you to maintain pressure during attack sequences. And they be used to extend combos, canceling Special Moves to allow for extra hits and damage.
Focus Attacks are performed the exact same way for every character: press Medium Punch and Medium Kick at the same time. Pressing the buttons down starts the character performing a "Focus." This is the Focus Phase. You can continue to hold the two buttons down for the character to remain in the Focus Phase for a period of time. As soon as the two buttons are released, the character will perform an attack, which is a fixed attack for every character. This is the Attack Phase.
The Focus Phase
While holding the two buttons down, your character will remain in the Focus Phase for a limited amount of time. During the Focus Phase, there are two distinctive traits.
Building Up a Focus Attack
The first trait is that your character will "build up" strength and, after a short period of time, flash white once and then, after another small period of time, flash white once more and immediately go into the Attack Phase automatically. The flashes indicate the "level" you have built your Focus up to. The entire time you start the Focus and before the first flash, you are considered at Level 1 Focus. Between the first and second flashes, you are in Level 2 Focus. Once the second flash occurs, you are considered at Level 3 Focus and will automatically unleash your attack. These levels result in you performing that level of a Focus Attack if you let go of the buttons.
The time it takes to reach a Level 2 and Level 3 Focus Attack is not exactly the same for every character -- some characters increase in levels quicker than others -- but, in general, the times aren't that far off. There are no characters that take an extraordinarily long time to charge to a Level 2, for example. Nor is there a character that gets to Level 2 almost instantly.
Focusing an Attack
The second trait is that, throughout the entire Focus Phase, your character is capable of absorbing one hit from your opponent. This is referred to as "Focusing" an attack. This attack can be any single hit, such as Guile's Standing Hard Punch, Chun Li's Jumping Hard Kick, Rufus's Falcon Kick (dive kick from the air), Ryu's Hadoken, Balrog's Dash Straight, Cammy's Cannon Spike, or a Level 1 Focus Attack.
As soon as you Focus an attack, the damage the move would normally do is also absorbed... to an extent. Instead of taking the damage straight up, you end up taking that amount of damage in "White Damage" (see White Damage section in Game Systems). So technically, you can gain that life back if you are not struck again any time soon.
However, one hit is all you can Focus. If you continue to hold your Focus and the opponent manages to hit you with two hits total, the second hit will make you leave your Focus and go into Hit Stun like any normal move hitting you. And it doesn't matter what strength the moves are: it's any two hits. This could be a Jump Attack followed by a Shoryuken, two Standing Light Punches, or a two-hit Move like Ryu's Solar Plexus Strike. You'll still absorb the first hit, but as soon as the second hit connects, the Focus is done.
It's also worth noting that all Armor Breakers will defeat Focus Attacks instantly on their first hit (see Armor Breakers section in Universal Abilities). Also, Throws will work on anyone while they are Focusing.
Dash Canceling the Focus
At any point during the Focus Phase, as long as you are still holding the two Medium Attack buttons down, you can actually cancel the Focus with either a Forward Dash or a Back Dash. Otherwise, the only way you can exit the Focus Phase is to go into the Attack Phase.
It should also be noted that the Dashes "correct" themselves. If, during the Focus Phase, the enemy manages to get to the other side of you, Forward Dash will still be tapping twice towards the opponent even though you are facing backwards and Back Dash will be tapping twice in the direction you are facing.
Focusing Proximity
Another peculiar quality about the Focus Phase is that, even though you are not attacking, the game treats you as if you were. In other words, as long as you remain in the Focus Phase, the opponent, if close enough, is forced into Block Animation and they cannot walk backwards. It's worth noting that the field of influence of the Focus Phase is pretty large, so you can be almost a half a screen's distance away and still be close enough to be forced into a Block Animation.
The Attack Phase
Each character has only one Focus Attack and, between the characters, these attacks vary in range and speed and some have extra abilities. Guy, for example, has a very far ranged Focus Attack. Balrog's Focus Attack is very short ranged. C. Viper's Focus Attack is particularly slow while Fei Long's Focus Attack is really fast. And Juri's Focus Attack has the ability to jump over moves that hit too low.
If you leave the Focus Phase by letting go of the two Medium Attack buttons and go into the Attack Phase, you lose the ability to absorb a hit during the animation of the Focus Attack. So if the opponent just happens to attack and you let go of the Focus before your opponent's move hits you, your Focus Attack will lose out if it catches you during your attack animation.
The Levels of the Focus Attack
As mentioned in the Focus Phase section, you have three different levels of Focus Attacks depending on how long you charged your Focus for. However, all three levels of Focus Attack share one common trait: the Attack can be canceled into a Forward Dash or a Back Dash when the Attack connects against the opponent. This can be used to continue pressure on block or continue a combo on hit with a Forward Dash or to run away after the move connects with a Back Dash.
Level 1 Focus Attacks are pretty much just like a Normal Move. When they hit an opponent, the opponent goes into Hit Stun for a short period of time. The Block Stun caused by a Level 1 Focus Attack isn't very long, so if you make your opponent Block a Level 1 Focus and you cancel into a Forward Dash, most characters are at a Frame Disadvantage (See Frame Advantage section in Advanced Techniques and Concepts) after their Dash has completed.
Level 2 Focus Attacks do more damage to the opponent when they hit and cause the victim to go into Crumple Stun (see Crumple Stun section in Game Systems). So if you cancel the Level 2 Focus into a Forward Dash, you get a free ground combo of choice. On Block, Level 2 Focus Attacks also cause more Block Stun than a Level 1 Focus. So if the opponent blocks it and you cancel into a Forward Dash, most characters have a very small Frame Advantage at the end of their Dash.
A Level 3 Focus Attack also causes Crumple Stun, but, most significantly, they become unblockable and are also considered Armor Breakers! Also, the initial impact freeze from a Level 3 Focus Attack is longer than that of a Level 2. That means the opponent starts their crumpling animation slightly later and, thus, you have more time to hit the opponent before they are considered airborne during their crumple (again, see Crumple Stun section in Game Systems). For example, on a Level 3 Focus Attack Crumple Stun, C. Viper can cancel the Focus Attack with a Forward Dash and combo into an immediate EX Thunder Knuckle and have the opponent get hit while grounded. However, on a Level 2 Focus Attack Crumple Stun, the Forward Dash into EX Thunder Knuckle is too slow so that the Thunder Knuckle connects on the opponent when they are considered airborne so it ends up popping them into the air.
And finally, one extra benefit of a Level 3 Focus Attack is that the ability to absorb a hit during the Focus Phase is transferred to the attack if you had not absorbed a hit during the Focus Phase. If that's the case, if the opponent attacks you with a non-Armor Breaking single hit move during your Level 3 Focus Attack, you'll absorb it and nail the opponent. However, if you had absorbed a hit during the Focus Phase, your Level 3 Focus Attack can lose out to a single hit just like a Level 1 and Level 2 Focus Attack.
Anti-air Focus
Focus Attacks actually behave differently when striking the opponent out of the air. Level 1 Focus Attacks are a standard Knock-Down attack that pop the opponent up a bit and then they drop to the ground near you. Level 2 Focus Attacks put the opponent into a Free Juggle State (see Free Juggle State section in Juggle Mechanics) but do not knock the opponent up as high as a Level 1 Focus Attack. Level 3 Focus Attacks also put the opponent into a Free Juggle State and knock them into the air for much longer that even a Level 1 Focus Attack, but they cause the opponent to go into a spiraling Air Reel animation and are launched clear across the screen.
Counter Hit Focus Attacks
Focus Attacks are also modified when they land as a Counter Hit (see Counter Hit section in Game Systems). When a Level 1 Focus hits the opponent as a Counter Hit, the effects are the same as when you land a regular Level 2 Focus Attack: the opponent goes into Crumple Stun. Level 2 Focus Attacks on Counter Hit behave the same as normal Level 3 Focus Attacks. Level 3 Focus Attacks, however, behave exactly the same on regular hit or Counter Hit. You only get the extra damage benefit.
On Counter Hit, the only difference Level 1 Focus Attacks have when they hit the opponent out of the air is that the opponent actually freezes in place from the impact longer, which means you have a bigger window to Juggle the opponent if cancel the Focus Attack into a Dash. Level 2 Focus Attacks, like the Level 1 Focus Attacks, cause the opponent to freeze longer in the air from the impact. However, they now go into the spiraling Air Reel animation although they still maintain the same trajectory and are not launched across the screen. Level 3 Focus Attacks that connect on an airborne opponent on Counter Hit behave exactly the same as on a regular hit, even down to the impact freeze.