In this game if someone jumps in at you with a punch (forcing you to stand block because it is an overhead), your character is 'jailed' in a stand block animation even if you are crouching OR standing until the block string that follows the Jump-In Punch ends.
Fuzzy-Guarding is the idea that you are blocking correctly (stand for overheads, crouch for lows) despite that the animation of your character appears that you are standing our crouching throughout the entire duration of a block string depending on the (stand or crouch) state you were in when the block string began.
This is useful with certain strings in the game (ex: Sonya's 114).
If Sonya were to walk up to an opponent and press 114, the 11 portion of that string would whiff if they were crouch blocking leaving Sonya to be punished potentially.
If Sonya begins this string after a Jump-In Punch (Forces the opponent to stand block the JIP), then immediately enters the 114 string; The opponent must block the entirety of the 114 string until they can counter-attack (because the opponent is jailed in the stand-block animation).
If Scorpion were to do a Jump-In Punch (Forcing the opponent to stand block the JIP), then use the 11b4 string (b4 being a low), the opponents hitbox will appear as if they are standing even during the low, but is fuzzy-guarded appropriately if the opponent was holding down + block during the low portion of that string.
As you are put into block strings, press down then let go of down and press down again. You'll notice that your character does not actually appear to stand/crouch (change states) for the entirety of that block string (despite that you actually are blocking high/low as you are standing or crouching appropriately).
