left hook

noun2

1. •
   A powerful punch thrown with the left hand, typically after a jab or a straight punch.

   • I hit Stephens with a left hook followed by a looping right hand and a pulverizing left hook that caught him right on the button. — 2000
2. •
   (figurative) A surprise assault.

   • Just when he thought that the cross-examination was over and he'd parried the questions successfully, one of the lawyers stood up and threw a left hook that left him spluttering.