Williams' lawyer, Harvey Steinberg, asked for the mistrial Monday just before opening statements were about to begin. He said he was only able to excuse two jurors instead of the three he was entitled to during jury selection.
Judge Andre L. Rudolph granted the request and scheduled another trial on the misdemeanor charges for Aug. 15.
Williams' trial has already been delayed several times, including last fall after he suffered a dislocated right elbow during a game.
He faces a multiple-game suspension from the league because it was his second such arrest in his seven seasons in Denver. The Broncos stripped him of his captain's title shortly after his arrest on Nov. 12, 2010.
Police say Williams was pulled over a little before 3 a.m., when he was spotted driving his car without headlights. He was cited with DUI and taken to a detox facility.
He was fined an undisclosed amount by the team.
Copyright 2012 by The Associated Press