According to Nationals manager Davey Johnson, the team was at a luncheon and was warned that traffic would be bad because of an immigration rally at the Capitol.
"I'm sure the umpires were not aware of it and got caught up in it," Johnson said. "The bus driver [at the Nationals luncheon] could not go near the rally. We just went all around just getting out of there."
Ron Kulpa, Tom Hallion, Phil Cuzzi and Chris Guccione made up the umpiring crew and they were not available for comment.
The delay did not bother Nationals starter Jordan Zimmermann, who pitched seven solid innings and allowed two runs on seven hits. White Sox starter Gavin Floyd also started strong, limiting the Nats to one hit in the first three innings before Washington's lineup chased him in the sixth.
It helped that the umpires called 40 minutes before the game to warn that there would be a delay.
"They said they were a mile away, but they took forever," Johnson said.