The shooter wounded multiple people early Wednesday, including Majority Whip Rep. Steve Scalise, who was shot in the hip, and a staff member from the office of Rep. Roger Williams, R-Texas.
Scalise is undergoing surgery.
Rep. Rand Paul, R.-Ky., and Rep. Mo Brooks, R.-Ala., who were both at the baseball field, described the weapon used by the shooter as a rifle. Paul said he heard a first, “isolated” shot followed by a “rapid succession” of five to 10 shots.
Capitol Police and Alexandria police officers who responded to the scene exchanged fire with the shooter, according to Capitol Police Chief Matthew Verderosa.
—CNBC’s Jacob Pramuk contributed to this report