Dukes was late because he was signing autographs at a Little League function that was not sponsored by the Nationals.
Both acting general manager Mike Rizzo and manager Manny Acta made the decision to let Dukes sit out the game, and the outfielder was warned that if he was late again, he would be optioned to Triple-A Syracuse.
Dukes did enter the game in the eighth inning after Roger Bernadina fractured his right leg. Dukes ended up going 0-for-2 in the game, dropping his batting average to .323.
"We are going to change the culture here, regardless of how well a guy is playing," Acta said. "It was a bizarre situation, because he was doing something that we encourage our players to do. He was out in the community doing something for some Little League program and he just showed up late for work.
"He was very remorseful about it. He felt bad, but we have to lay down the law. Regardless of who is out there, we are still losing ballgames. We have to change the culture somehow."
This is the second time Dukes was late for work since he joined the Nationals, the first coming on Aug. 2, 2008. Although he was scratched from the lineup that day, Dukes was able to get into the game in the sixth inning against the Reds, but he left after the eighth, hampered by a cramp in his right calf.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.