Japan's Ryota Murata retained the World Boxing Association middleweight crown on Monday with a fifth-round stoppage of Canadian challenger Steven Butler.The London Olympic Games gold medalist secured the victory by technical knockout after dropping his opponent in the closing seconds of the round at Yokohama Arena."I felt good while I was in the room waiting to come out and I thought I'd be able to end it quickly," said the 33-year-old Murata, who improved to 16-2 with 13 knockouts.Making his first defense since reclaiming the belt in a rematch with American Rob Brant in July, Murata fought…READ FULL ARTICLE