Speed Blitz is the act of one attacking their opponent before they are capable of perceiving or reacting to them. Blitzing is different than outpacing, where a character is simply faster than the other. A blitz is more like an all around outclassing in speed.
One somewhat similar example of a "blitz" in real life would be a person getting shot. As the bullet moves at such a fast pace, the victim is unable to react to or even see the bullet coming at them.
Originating as a nickname VS forum users would give to a certain technique they noticed in various superhuman fight scenes, the term speed blitz has since been a more widespread saying used to describe a popular trope in media.
However, frequently characters in fictional fights will refrain from blitzing. Either due to the character's personality, or plot/character induced stupidity. Or the simple fact that a fight scene would not be entertaining if it was concluded far before the audience could blink.
In a Versus Match Up, free from limitations like plot or character induced stupidity, blitzing is a much more considerable outcome of a fight. Especially when characters are under a state of bloodlust.
Though, just like how a fight scene could potentially be bland and boring due to characters blitzing, a match where one character can blitz the other often doesn't allow for much discussion or debate. And pretty much takes away the majority of one's arsenal, strategies, skills and abilities if someone can just kill them before they get the chance to use them. On top of resulting in a stomp/spite match more often then not.
In order to prevent such a predicament, some VS discussions may be open to equalizing speed. In an attempt to make the topic more balanced, debatable or engaging. But it can often be difficult to pinpoint when exactly a speed advantage constitutes a "blitz." So instead such decision is mostly given on a case by case basis and using common sense.
The video below is a fairly accurate representation of what a speed blitz would look like in a practical fight: