Well before the end of the baseball game, authorities "discovered a generator that appears to have exploded inside a construction site in the 1200 block of First Street SE," the D.C. Fire and Emergency Medical Services Department said.
Later in a Tweet, the fire department said "the incident involved (an) underground power vault." Such devices often house transformers, used for stepping down electrical voltage, and it was unclear whether the explosion involved a transformer rather than a generator.
As of perhaps a half hour after the explosion, the department said there was no fire or smoke, and no power outage had been reported.
As exciting as the game may have been, the attention of some fans was at least briefly and understandably distracted by the big bang nearby.
"Yeah," said Hillary Jett "You heard a loud bang from inside the park and the lights flickered."
It seemed to come from near the centerfield exit said Jas Taylor, who reported a "loud boom" and also said a "fireball was visible." Daniel Kimbro, another spectator, also said he saw a fireball.