Fighter KO's opponent when he was walking back to his corner

MMA fighter Murthel Groenhart defeated his opponent, Harut Grigorian by knocking him out while he was walking back unguarded to his corner in the second round at the Glory 42. Grigorian had been hit by Groenhart's knee kick following which he let his guard down and walked towards his corner. The knockout which was widely called 'unfair' was, however, legal.