Gassiev did land an overhand right and Usyk reacted with obvious discomfort. He clinched immediately. He was hurt.
Everybody has a glass jaw you dimwit. No human being can take a 200 plus pound highly trained mans fist being rammed into their own skull as hard as possible and not react to it.
Ever heard of George Chuvalo, Oliver McCall, Marvin Hagler, or Jake LaMotta?? SOME fighters DO have good punch resistance. And, there are many others who can't stand up to a good shot, and this needs to be factored in when assessing their performance on hypothetical matchups, their career records, etc. etc. CHINS MATTER. If you can't take a good shot, all things being equal, you're not going to go far in this sport.
Some fighters have better chins than others yes. But all fighters have fragile chins. Its simply anatomy. You can't ram a closed fist into a human skull over and over again without causing damage.
Anybody that voted "we don't know" - you don't, maybe. Some of us do. Listen to your betters. The correct answer is "no".
until his defence hold up we may never know...like Mayweather,well Mosley have a KD against him but that doen't prove it either...
No, you're making that up. (or, to be charitable, misremembering) There has been exactly one thread made on here in the month of December wherein Usyk's chin was discussed, and nobody mentioned a thing about him getting knocked out because that has never happened. https://www.boxingforum24.com/threads/usyks-chin.678547/
I don't think he has a bad chin but in his two fights at heavyweight he's never really been tagged. Joshua seemed to have hurt him a little once but never followed up and Chisora well,,,,,,wasn't much going on there.