Sacked, as in the past tense of the verb "to sack", is a term used in the sport of North American football. If this was the context in which you heard the term, let me know, and I'll explain further what it means. Without getting into too much detail right now, it refers to the quarterback of one team being tackled by a defensive player of the opposing team, before the quarterback has thrown the ball, during a play. The defense would want to do that, because doing so will end the offensive play.