At least five people were taken to hospitals from the incident, according to Alexandria Police Chief Michael Brown.
The shooter is in police custody, according to CNN. He was taken to a hospital after the shooting.
The first shot was an isolated shot, Paul said, but “it was pretty loud and pretty close.”
“After that we heard a succession of shots -- five, 10, 15 shots in a row,” Paul said.
Paul said he thought the shots were coming from the third base line, but he was unsure of the location of the shooter or how many people could be behind weapons.
“I couldn’t see the shooter, but I wasn’t positive, ‘Am I standing on the right side of the tree or the wrong side of the tree?’ And I’m looking around trying to determine if there’s one shooter or two shooters,” Paul said.
He said he noticed one of the staffers had been hit in right field, and he asked another staff member if he wanted “to try to get out.”
“And all of a sudden he was up, and he was over the 20-foot fence in about two seconds,” Paul said. “I’ve never seen anybody climb a fence that fast in my life.”
The shots stopped at one point, as if the gunman was reloading, but more shots rang out shortly after the pause, Paul said.
“I felt like ... my instinct was that he was moving, and that he could just move around the entire field and shoot everybody,” Paul said. “At that point, we decided to make a run for it.
“He was hitting the dirt around us out in right field, so it was a risk to stay and a risk to go, but we chose to go ahead and make a run for it, and we had to climb a couple more fences at that point to get out.”
In a Wednesday news conference, Tim Slater, FBI special agent in charge, said the incident will be investigated with “state and local partners.”
Slater said it is too early to tell if the shooting was an assassination attempt or an act of terrorism.