I enjoy talking/thinking about SFA3 a lot, dunno why.
When recovering in the air in SFA3 there's actually 3 types, plus a 4th for rolling. Forward, neutral, back air recovery puts you into a temporary invulnerable state. However, during this invulnerability time you are unable to act (which includes blocking).
Whether on purpose or by accident, however, the amount of time you are unable to act is longer than the invulnerability duration. That means that after teching you are invincible for several frames, then you are no longer invincible and still unable to do anything other than super/VC activate.
This is how tech trapping in SFA3 works, entirely.
Basically, the game's juggle system makes it so that the opponent can air tech any time the player is not currently performing an action or during the last frames of recovery from a move (this is called "neutral"-state, though the term "neutral" is very misleading). V-ism allows you to enter a custom combo state which allows you to cancel attacks into another attack, therefor you can constantly be in a state of action by chaining move after move. But this also means that you can't stop or they will be able to tech, and in order to jump you must stop.
Therefor, players adjusted the enders to their combos to end with a setup that will allow them to recover very very quickly, as well as hit the opponent one last time to position them in the air where they want them to be. This way, for example, I will throw out a light attack that recovers very quickly and pushes you above head level, then perform a quick jumping attack. Now, if you don't tech then my jumping attack will connect, and even if you do tech you will still be in range for my jumping attack to hit you as soon as you become vulnerable again.
Therefor, it hardly matters what you decide to do, except that in by teching you are resetting the combo count, which also resets damage scaling, making whatever I do next cause significantly more damage.
Now, technically when you land you enter a recovery state, because jumps have recovery frames on landing. But, Capcom implemented a little thing that made it so that you could cancel this recovery state with a defensive crouch (low block). The reason they did this was because they wanted players to at least be able to block sweeps right as they touch the ground, hence why it's referred to as "trip-guard".
This gave rise to "crouch cancelling" and "walk cancelling". Walk cancelling is actually just a crouch cancel, except that you do not jump after crouching, and instead walk either forwards or backwards after crouching. Oddly, walking is considered an action. The only reason you can't transition from an attack into a walk is because the attack itself has a recovery period which triggers the "neutral" state.
A couple of random notes:
Air teching in SFA3 can be performed semi-automatically. A lot of players try to mash techs or time techs, but this is not necessary. Instead, you can hold the inputs for a tech after the last hit of a combo, before the neutral state begins, and the game will automatically tech for you. For example, if you are trapped in Sakura's crouch cancel series, if you push the tech inputs and hold it on the first j.FP attack you will not tech at the end of the series. However, if you wait until the last j.FP of the series and then push it any time between the tech window and the end of hit-stop occurrence, then you will automatically tech on the first frame of "neutral".
Many throws and airthrows bypass damage scaling entirely. Even if the combo count is over 60 hits and any move you do is causing 1 pixel of damage, certain throws that have been dubbed "slam" throws will simply ignore damage scaling and cause their usual chunk of damage (making them ideal enders).
Juli is a bit fucked in this department. While Cammy and Juni have the hooligan combination special move that can grab airborne opponents and cause slam damage, Juli does not. Therefor it may seem like a good idea to go for a kick-airthrow ender, but this is not the case. The reason is because the kick-airthrow has such massive recovery even when not teched that it is often highly punishable.
Pressing inputs at the point of hit occurrence will cause you to flash pink. This is actually a damage reduction mechanic like in Melty Blood, and will reduce damage by 50%. This also occurs during block-stop, when you flash blue, it reduces the amount of guard meter damage you incur. It may also have an effect on chip damage, but I doubt it.
Command throws break a lot of rules during V-ism's VC custom mode. It's well known that they are able to allow certain command throws to pick the opponent up off the ground (OTG). However, it's sometimes overlooked/downplayed that they can also grab the opponent during other states that they should not be able to, such as blockstun, hitstun, and during jump startup frames (where you are normally immune to throws).
This doesn't sound particularly threatening until you consider the application of crossups being followed by an immediate command grab, or even a unactivated crossup followed by an activation followed by a command grab. Imagine the scenario of any time you are knocked down, the opponent does a deep crossup that can't be hit by reversals (because the reversal goes the "Wrong way", and is ambiguous and difficult to block in the first place) followed by an activation into command throw that blows through alpha counters. And then, of course, cancels the command throw into a custom combo that takes you to the corner, and then sets up a tech trap into infinite death.
Say hello to Karin's potential. And you thought anti-air VC's were scary huh.
Regarding tech traps though, there are exactly two characters that can transition from a ground-based VC into a jump juggle. That would be Chun-Li, who cheats, and Rolento.
Rolento's transition from ground to air is hardly so esoteric as Chun's. Being that his super jump counts as a special, he can cancel his normals and specials into the super jump.
But it's apparent that Chun-Li cheats when observing the technicals of HSFA (hyper street fighter alpha) that is bundled in SFAA (street fighter alpha anthology). Reason being, the HSFA mode allows SFA3 characters to battle against SFA1 and SFA2 characters. The SFA1 characters have the interesting property of becoming instantly invulnerable to further juggles the instant the opponent hits neutral. In this version, although it's still technically accurate to the SFA3 arcade version, Chun-Li is not able to perform her transition on the SFA1 characters, therefor she must at some point enter a neutral state.
However, in vanilla SFA3 and arcade SFA3, it is literally impossible to air recover from her c.SK, [d]u-SK, SK, jump VC.
The only real consolation to this is that it has to be done off a crossup since generally the tenshou kyaku will whiff otherwise. And, because her crossup is a j.SK, she doesn't get to do a whole lot of initial damage because the damage scaling from the light attacks in the setup is pretty big. Of course, if she infinites you, it hardly matters.
The sides in SFA3 are uneven. Player 2 will crossup a cornered opponent during a crouch cancel series due to the uneven sides. This will prevent basic crouch cancel series. However, there's a few ways to negate this. First, quite a few crouch cancel series and infinites can be performed by simply jumping vertically instead of diagonally. This is of course much harder, but still possible. Also, it's possible for many characters that have infinites to perform them anyway simply by using a crossup during the side switch, then continue the crouch cancel series by jumping across the screen while juggling, and then loop it back by using the crossup again.
Of course, these are not options for every character, but they are options for at least several.
The uneven sides thing also occurs when special moves are involved. If you perform a special move that takes you "into" the corner, you can crossup or crossunder a cornered opponent. This isn't particularly useful for many characters, but it most certainly is very handy for specific characters.
Oh, did I mention that slam throw damage also ignores the damage reduction from tech-hitting a throw? Well, it's true. You can't negate slam damage.
The shadows that trail along with you during a V-ism VC retain the move blockability properties. This includes high and low. And since they are technically mimicking you with a slight delay, it is possible to make the shadow connect with a high attack while you hit you a low attack, thus creating another form of unblockable.
This is particularly useful midscreen, once again, due to crossup. With VC1 active (the shortest duration between you and your shadow) you can crossup then immediately hit low while the shadow hits high. Technically this can be blocked by a computer or TA tool. But, humans can't normally block high, low, high, low within a matter of frames between each hit, which is the exact sequence you have to deal with.
These crossup types are particularly strong because it is possible to overshoot the opponent right as they are getting up, causing any reversal that they do to be facing forward and "under" you, which means reversal DPs and such whiff entirely because they move/face the "Wrong" way.
So, combine that with the command throw unblockables, and you can see why crossups are pretty scary.
There's really only a few characters that can escape a perfectly executed Chun-Li midscreen crossup unblockable.
Akuma should be an obvious one, teleport. Juni and V-Dan aren't as blatantly obvious, but they can with a well timed pushblock. I use to have a list of who exactly could and could not do it, but I realized the list was pretty obsolete when I realized the exact list did not apply to crossup cmd throw unblockables in every case.
Despite all that, confusion/mixup VCs are still very effective. Especially when the user can resort to causing massive chip and/or a guard crush when the mixup fails.
There's a bizarre "glitch" that occurs with Chun-Li j.d-FK "stomp" when canceled into a VC. When performed while rising into the air, Chun will continue on that path even when the VC is activated. However, if done while descending then Chun will actually retain the trajectory, if slightly altered to make her fall even faster. This gives her an auto-confirm for her unblockable. Basically, if you perform a meaty stomp and the stop whiffs or you get hit then you don't technically waste any meter. If, however, the stomp hits or is blocked then you will cancel into the VC and can perform an immediate j.SK followed by the c.SK for the unblockable. This isn't particularly useful midscreen though, since technically the stomp either can't crossup or has a very very difficult time of doing so even when it's possible. Therefor the best application for it is when you have the opponent cornered. This technique can be reversed in that situation, but thanks to the fact that it's an auto-confirm, at least you won't be gambling with your meter.
Gen's Jakouha super is also another little rule breaker. The grab will actually break any and all juggle and invulnerability state rules. Basically, if the opponent is in the air and Gen collides with them, they will get grabbed. To boot, the damn thing is a slam throw, and therefor ignores damage scaling as well. This was fixed in the old console versions and added in as a dipswitch in SFAA. But in SFA3 he is the only character in the game that can break juggle limits and aerial invulnerability states. He can even grab you when you're in hit-reel from an alpha counter.
For many years the top tiers have been considered to be Akuma, Sakura, Dhalsim, and Zangief. Which is pretty cool since none of those characters possess infinites. And Dhalsim is considered to hold that place in the tiers in any of the 3 -isms.
Unfortunately, times have changed, players evolved, etc. and poor Zangief no longer holds his ground there. Sodom has been secured as one of the top 4, but it's actually debatable if the S class should be limited to just 4, since Sagat is generally also considered to be ranked on the same level as the others. I personally wouldn't be surprised if Vega(claw) and Karin make their way in there some day, but for the time being this is not the case.
So, it just goes to show that normals, functionality, and utility can conquer "the infinites". I mean, after all, Birdie is generally ranked dead last in everybodies tier lists for that game, and ironically he does have an infinite.
Ok, so now this post is entirely too long.