OH ok I understand. The man who did that was Gregor Clegane. He is the guy who got mad when he lost the joust horse tournament. He was angry and just started killing people randomly. Eddard Stark saw this as an opportunity to politically attack the Lannister family since they have been making moves against his House (stark). Since Gregor Clegane is a bannerman to House Lannister (he pledged his house, a minor house, to Lannister) his actions cause also house Lannister to be at fault. Eddard told the court that Tywin Lannister (father of Jaime Lannister and leader of house Lannister) that if Tywin does not appear before the court in two weeks to answer for the fault of his bannerman and help capture his bannerman, then he will be branded as an enemy of the crown.