Blood debt

A Blood debt is a Klingon custom in which, after being dishonored, a Klingon warrior seeks to regain his honor by killing the person responsible for their dishonor.

In 2254 Christopher Pike received a blood debt from Kaaj, Son of Torg following the Klingon's humiliating defeat at the Pharos siteworld. (EV comic: The Fires of Pharos)