PREFACE: let me note that my description is based on my pre-TWC Wing Chun experience. TWC is obviously different in many ways, not just in some of the functional methodology but how it is taught (Sifu Keith taking the classic, man sau /wu stance and saying "no one really fights like this..."). Also let me note this, the previous WC I took was a WSLVT under a student of Gary Lam. That had "standing grappling" but that was largely a more "firm" method of trapping so one could strike. I do think WC period is good against a dedicated striking art, so long as you can get your opponent to play "your game", in other words pray you aren't fighting a Mayweather who is so good at dancing you can't maintain the "blitz" (more on the "blitz" later). I won't get into grappling right now because this would become a novel.
THAT SAID:
In my experience there is a distinct difference in a street fight and by that I mean someone suddenly trying to rob you, someone looking to outright assault you. You can have a street fight that is a stereotypical competition, such as two drunk idiots facing off at a bar but they are both very different. Let me explain.
In a stereotypical competition (or the bar fight), for lack of a better term, you are looking to win. You win by either points in a competition or by pounding the other guy into the ground so that he can no longer fight in both. You have the sizing up phase, everybody knows it's coming, and because of that people fight typically in a more reason door controlled fashion, though you are correct in that this is not always the case. They test each other they might use a strategy of softening the other person up things like that.
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In the assault, robbery street fight type scenario there is no testing you need to go all in everybody goes all-in right out of the gate. It's basically a "blitz attack" art (told you I would get there
), even the defenses are not simply about protecting, or even injuring (as some arts do) but wedging your way in to attack. This method is much more suited to either A) the street attacks I noted OR B) the competition method you note.
If it becomes a more "strategic" (meaning the testing, measuring etc) it is at a disadvantage. On the street, in the best case scenario, you knockout/cripple your opponent BUT even if your opponent is still capable of fighting BUT you've knocked him on his ***, injured him to the point they won't chase you or say "okay this isnt worth it", thus giving yourself the opportunity to escape you win, unlike a competition where you .
Think of it like Warfare. There are many types of warfare and the tactics are different as well as the tools. So to me Wing Chun is like guerrilla warfare where it's good enough to just hurt your enemy really bad and get out ASAP. This is different from conventional Warfare which is about not only winning the individual battle but also winning the ground on which that battle was fought (you stay they leave). Now sometimes in guerrilla warfare you hit so hard against the opponent that you do actually manage to control the land when everything is said and done but that is the best case scenario, as I said.
Hope this explains a bit better where I am coming from.