Here is a quick long guide to SFHD throw properties! 
(The two basic types of throws are normal (or regular) throws and command throws. If I write just “throw,” I usually mean all throws. I tried to remember to write in exceptions for command throws as needed, or write “normal throw” or “regular throw” when I mean to refer to those exclusively.)
Throws can be done by pressing towards or away on the joystick within range, and the fierce punch button. Some characters can also throw with any combination of the strong, forward, and roundhouse buttons. Air throws are done in the same way.
- I think you can also press up for some airthrows.
Command throws require some sort of “special attack” joystick motion followed by any punch button.
- The exception is Akuma’s super, which has its own specific input.
Each throw has a different range at which it can be used. This is a maximum distance that the opponent can be to you for the throw to be successful.
- I don’t know it this goes by vulnerability hitboxes or just by character “centers.”
Throws come out (occur) instantaneously; they have zero startup time.
You can throw any time that you are in the standing state. Air throws require that you are in the middle of a jump, you are not currently executing any sort of attack, and you haven’t been hit during that jump.
- I’m not sure if you can do an (early) attack in the air, recover from it before you land, and then do an air throw during the same jump.
You can throw someone who is standing or crouching, blocking high or low, or who is in the middle of a move on the ground.
- Two exceptions to that: 1, you cannot throw someone who is currently within the invincibility time of a special or super move that has a period of invincibility. 2, Akuma’s super is uniquely unable to throw someone during their jump-startup. Jump-startup is the very short period of time (3-5 frames I think, depends on the character) where they’ve already pressed up (or up-towards or up-away), and they are still standing and haven’t left the ground yet, but they will jump at the end of that startup time.
You cannot throw someone who is: in blockstun, in hitstun, or airborne (exception being air throws, where you must also be airborne). Note that there are a couple moves, and sometimes just parts (time-wise) of moves where the character does appear to leave the ground but they are still technically on the ground.
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The exception is air throws, which can only be done on opponents who are in midair–whether they’re currently in the middle of a move or not–and have not yet been hit during their jump.
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The exception to that exception is Vega’s walldive airthrow, which works successfully whether the opponent is on the ground or not.
When someone is thrown with a normal throw, if they press either towards or away and either strong, fierce, forward kick, or roundhouse (note that these are all commands for doing their own normal throw) within 13 frames of when their attacker’s throw took effect, they can “Tech Hit,” or soften it. That is, they will land on their feet rather than being knocked down, and they will only take half damage. Note that command throws cannot be softened.
(Regular) throws are considered to have no recovery because if they are unsuccessful, you just see an attack come out (usually a normal attack, or a command attack if applicable, or for Vega’s walldive attack for a missed walldive throw). In terms of game mechanics, the successful throw input beats any normal attack or command attack inputs. Of course, the attack obviously comes out only if you were already in a state where doing the attack was possible. Note that these “accidental” attacks do have their recovery time.
- The exception is that some command throws do actually have “whiff” animations. As they, like all throws, have no startup time, you only see these animations when the throw misses; the opponent was not within range, or was in an unthrowable state. Note that these animations are just a visual representation of its recovery time; the throw itself only has a chance of occuring on the first frame. That is, when you try throwing unsuccessfully and get a whiff animation, if the opponent becomes throwable (enters the range or changes to a now-throwable state) the throw still does not happen. - The exception to that is Akuma’s super, which remains “active” (able to throw) for an extended period of time, not just the first frame.
If a throw’s input is overlapped by the input for a special attack, the special attack will “come out” instead of the throw. Example: Ryu’s down down-toward toward and fierce punch within his throw range will give a fireball instead of a throw. Note that this is why command throws will come out over (regular) ones when applicable.
- The exception to this is command throws, which are considered special attacks, and as such follow the ordered list of preference of each character for determining which special attack occurs when the inputs for multiple special attacks have overlapped. Example: Zangief’s lariats happen over his SPD which happen over the banishing fist.
Note that any of a character’s cancelable normal can be cancelled into a command throw, just like any other attack.
A throw will never trade with or beat any active attack. If an opponent’s attack hits you on the same frame that you would’ve otherwise successfully thrown your oponent, the attack wins and no throw occurs.
- The exception to that is Akuma’s super, which has a a lot of invincibility time. In this case, it will “beat” all sorts of attacks simply because they cannot hit hit at all during that period of time.
If two players execute a throw against each other on the same frame where they would both be successful, the game randomly chooses which one actually gets the throw.
- I believe he exception to this is command throws. If a command throw and a normal throw are executed against each other simultaneously, the command throw will always win.
- I think that the determination is also random when two command throws occur simultaneously, but I’m not positive. There maayyyy be a pecking order.
Semi-relevant note: When two buttons are used simultaneously, each of which would result in the same class of move (two normals, two regular throws, two command attacks, whatever), there is a pecking-order they all follow of which will actually occur and which is ignored.
*I have no idea what the order actually is. Example, may not even be correct: You press jab and short at the same time, the jab occurs instead of the short. You press strong and fierce at the same time, the strong occurs and the jab does not. Remember, however, that if they would result in two different classes of moves, the “higher” class occurs instead: normal attack > command attack [ (successful) normal throw > special attack (including command throws) > super combo.
With the exception of any obvious changes (like Akuma’s super), all of this should apply exactly to vanilla ST as well. Actually, I beliiiieve that this is universal for all SF2 games.
Anything I didn’t feel sure about was marked with an asterisk. Any help with these uncertainties or corrections to shit I’m just plain wrong about are welcome and appreciated.