glass jaw

Etymology
An allusion to glass being easily breakable.

Noun

 * 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 s).
 * 2)  A vulnerability of that sort; a weak spot.
 * 1)  A vulnerability of that sort; a weak spot.
 * 1)  A vulnerability of that sort; a weak spot.

Translations

 * Finnish:
 * German: Glaskinn