glass jaw

Noun

glass jaw (plural glass jaws)

1. A fighting vulnerability where one is easily knocked out via a single hard blow to the chin or jaw (due to lack of conditioning, insufficient training, or damage from past cerebral concussions).
   • "How was I to know that big ape had a glass jaw?"1989, Bryce Courtenay, The Power of One, →ISBN, page 109
   • Early in Ali's career, experts believed he had what's called a glass jaw—that he would fall after the first big punch. He was now proving that he could take a punch, but each punch chipped away at his health.[2010, Stephen Timblin, Muhammad Ali: King of the Ring, Sterling, →ISBN, page 101

   Synonyms:

   glass chin, bad chin

2. (figuratively) A vulnerability of that sort; a weak spot.
   • It is essential that a player be able to identify his glass jaw or his weak spot and learn to deal with it in actual competition.1979, M. LeVan Rhame, Jon Chalmers Niemeyer, Tennis Magic: Playing With a Full Deck, New York: Vantage Press, page 164
   • But if Obama does have a glass jaw, if his candidacy is a bubble waiting to be pricked, a strong Republican nominee like McCain is precisely the guy to do it.2008 February 13, Ross Douthat, “Obama's Glass Jaw?”, in The Atlantic, archived from the original on 12 Jun 2019

   Synonyms:

   Achilles heel, chink in the armor, kryptonite, soft spot, soft underbelly, vulnerability, weakness, weak spot