Glass Jaw in boxing is a term used to describe a boxer who has a vulnerability to a knockout punch.
The jaw may be excessively fragile and therefore susceptible to punches. The opposite of a glass jaw is a good boxer’s chin, which refers to a boxer who can withstand powerful punches without being knocked out.
A boxer with a glass jaw is often at risk of being knocked out early in a fight, even by punches that might not affect other fighters.