Happened on this site by chance while researching a "boxer's fracture" and spotted this thread and thought "ooh, I know this!! I'll register and stuff"

So.

Wing Chun(*) should work against trained fighters(+) just as much as it should against untrained fighters.

*Wing Chun is not nearly as unified as people make out Ip Man taught different students different stuff - whether for body size or fitness or whatever reason, so even his immediate students have occasionally VERY different views. Not only that, but while Ip Man is widely regarded as a very important figure in Wing Chun he was not the only Sifu around so there are still more styles knocking around. Different styles may train different ways.

+Trained fighter can be misleading... Most WC school's training programs would stuggle when faced with grapplers, or even other WC styles.

Those points clarified... Wing Chun has just as many methods of dealing with hooks, haymakers and uppercuts as it does against jabs, crosses and the sort of straight punch you find in many eastern martial arts.
-Big haymaker? Try a Dip Sau stepping into your opponents structure with a Fut Sau to the throat
-Hooks? That's where you Tan Sau comes in, and again chop them in the throat
-Belly shots or uppercuts? Gan Sau and Jut Sau are all good...
Chi Sau should be about looking for openings to strike - any strike, whether a WC strike or not, let you and your training partner learn more by mixing stuff up. Get lighter on your feet step round/past/through stuff, use soft style wing chun and hard style wing chun, through hooks, dodge...

Many schools of Wing Chun are very very very hung up on lineage an tradition - Ip Man wasn't, Ip Chun isn't and these two are considered the more important men within the art (certainly in the last few decades)... If you're learning as part of a JKD syllabus then you should be able to talk people into loosening up so you can get more out of things... even the forward Gung Lik elbow energy can be applied incredibly lightly - my Sifu regularly makes trips to Hong Kong where he teaches seminars and using this little trick has baffled many tradionalists...

I've only been doing Wing Chun for 4 years now (5 times a week mostly, but the last year only twice a week frown ), but in that time I've encountered many different takes on what is Wing Chun... certainly some of it I don't like - not because it doesn't work, but because it doesn't fight my fighting style. Some of it has very solid, but very slow footwork, some has very light footwork that sticks to the same structures so stays very stable.

The attacks following straight lines should ideally apply to you the defender, and the attacker should be free to throw in anything at all - even take down attempts, you should then use your Wing Chun and defend the centreline to defend and strike them.

Bah, I'd meant to speak more elloquently than this, but I'm really tired so I'll stop here and hope that some of it makes at least some sense... might re-write/edit in the morning.
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Hullo!
I do Wing Chun, BJJ, Muay Thai, and a little Submission Wrestling.