The suspect, James Hodgkinson, was killed when officers returned fire.
Here's what we know so far about those who were injured in the attack.
Hospital officials said Wednesday evening that Rep. Steve Scalise, R-Louisiana, was still in critical condition after being shot.
At the time of the shooting Scalise, the third highest-ranking member of the House of Representatives, was being protected by Capitol Police security detail. After news of the shooting spread on Wednesday, Scalise received many well wishes from his fellow Congress members on both sides of the aisle.
President Trump visited Scalise in the hospital on Wednesday, calling him a "fighter."
Mika, a lobbyist for Tyson Foods, was helping with practice when he was shot. He is still in the ICU in critical condition.
"While the attack today was a terrible surprise, Matt's presence on the ball field, helping longtime colleagues and friends was not," Mika's family said. "He is a very thoughtful, fun-loving person who is competitive and loyal; all things which contributed to his continued commitment to the Congressional Baseball Game."
Mika, a former college baseball and football player, has worked for Tyson for more than six years.
U.S. Capitol Police Officer Crystal Griner was shot in the ankle but is in good condition, according to U.S. Capitol Police Chief Matthew Verderosa. In addition to Scalise, President Donald Trump and first lady Melania Trump visited Griner and her wife in the hospital on Wednesday night.
Griner, 32, is a graduate of Hood College, who supplied a photo of her during her days as a basketball player to ABC.
Staffer Zack Barth
Houstonian among victims in violent Virginia shooting
Zack Barth, a legislative correspondent for Austin Congressman Roger Williams, was shot in the calf.
His father said he's OK, and Rep. Williams said that his staffer had already been released from the hospital and would make a full recovery.
The Houston man graduated from the University of Texas at Austin in 2015.
Related: More about Zack Barth
Rep. Roger Williams, R-Texas injured his leg and ankle diving to safety in the dugout, according to ABC News, but he was not shot.
NCCU grad called hero after shooting
Capitol Police Officer David Bailey received a minor injury but was not shot, according to U.S. Capitol Police Chief Matthew Verderosa. Bailey was treated and released.
Bailey is a 2007 graduate of North Carolina Central University, the school said.
Related: More about Officer David Bailey
ABC News contributed to this report.