Shortly after, he said, one person was found with what appeared to be a scrape on Potomac Avenue SE, and two others with apparent gunshot wounds were found at the Navy Yard subway station on Half Street SE.
The person found on Potomac Avenue, just south of the ballpark, was only described as an adult.
The two people found by rescuers at the subway station were both described as male, but their ages were not available.
Neither of those two appeared seriously injured, according to Maggiolo. One had an injury described as minor and the other had an injury that was not believed to be life-threatening, he said.
Based on available accounts, it appears they could have been found at the station and shot elsewhere.
On Twitter, DC police reported a shooting in the stadium area Saturday night at Half and O SW streets, where the most seriously injured victim was found.
Police said a shooting was confirmed there. They said they were looking for two people in connection with the shooting, a man and a woman. The man had a silver pistol, police said.
Half and O streets are approximately 500 feet west of the ballpark, which is on the east side of South Capitol Street. The intersection is in a residential area where shootings have been reported over the years, but few during games.
Last summer, a shooting outside the park left three people injured, including a fan who had left the game and was waiting for a rideshare vehicle.
The four victims on Saturday were found about an hour after the game between the Nationals and the New York Mets ended. It was unclear if any of those injured had been at the ballpark.
Attendance for the match, the third of the season, was listed at 21,369. The match was reported at 10:19 p.m.
At 10:56 p.m., firefighters were notified of the victim at Half and O streets, according to available accounts.
Many fans typically use the Navy Yard station to get to and from games.
The station is about half a mile from the site of the reported shooting. The site on Potomac Avenue SE where one of the victims was found is also about half a mile from the site of the reported shooting, but at the opposite end of the park from the subway station.