House Majority Whip Steve Scalise, who, along with a congressional staffer and members of the congressional police force, was injured during the shooting. Scalise's office later said he was in stable condition and undergoing surgery.
Following a volley of bullets shot at members during the practice, Rep. Mo Brooks took off his belt to assist a wounded aide.
"We used my belt to help put a tourniquet around his leg," Rep. Mo Brooks told CNN. "There's a guy with a gun blasting away. Fortunately, it was one of the good guys, one of our security detail who was shooting back."
Brooks added that they gave the Louisiana congressman liquids and put pressure on his hip.
Arizona Sen. Jeff Flake said he and Rep. Brad Wenstrup of Ohio, both in attendance on the scene, attended to Scalise as soon as they were able
"Somebody, finally after about 10 minutes, yelled, 'Shooter's down!' so I swing down to Steve and put pressure on the wound," Flake told CNN.
Wenstrup, a physician and an Iraq War veteran, told Fox News
, "I felt like I was back in Iraq but without my weapon ... Everyone just got down."
According to his fellow members of Congress, Wenstrup immediately administered medical attention.
"I held a cloth over the wound to stop the bleeding as Brad was getting some kind of scissors device to cut through the pants to try to have better access to Steve Scalise's wound and his hip," Brooks said on CNN.
"I put pressure on his wound in his hip," Brooks said, adding that Wenstrup started to focus on minimizing blood loss. "Shortly thereafter, the police showed up, and a helicopter landed in center field and took away whomever the folks decided was the most wounded, most critical."
'They showed incredible bravery'
The presence of Capitol Police members as well as individual members' security details were also largely credited with saving lives.
"It would have been a massacre" without the Capitol Police, Republican Kentucky Sen. Rand Paul told CNN.
Paul said that when the shooting began, he was the farthest away of anybody on the field but could see two staffers laying in the dirt on the ground and bullets were flying all around. After "at least 50-60 shots" had been fired from the shooter, he said he heard the Capitol Police respond.
"Nobody would have survived without the Capitol Hill police," Paul said. "Our lives were saved by the Capital Hill Police. Had they not been there, it would have been a massacre."
Paul continued to paint a bleak picture of the situation on the baseball field.
"The people in the dugout had no route of escape. Their only chance of survival was to get below the surface of the ground. And they were only 20 yards from the shooter," he said. "You are completely helpless -- having no self-defense and no way to get to somebody. The field was basically a killing field."
Flake said he saw a member of Scalise's security detail return fire on the gunman for what felt like 10 minutes, even though the police officer was wounded in the leg.
Rep. Joe Barton, who was team manager, told MSNBC, "Scalise's security detail immediately went in to return fire." Barton said he was hiding behind the dugout as "dozens if not hundreds of shots fired." His son, who was in attendance, was hiding behind an SUV.
Members were almost breathless as they described the heroism of Capitol Police members who continued to shoot at the attacker despite being injured themselves.
"The Capitol security guy, who had already been shot, who helped take down the shooter, came limping toward us in the outfield, totally ignoring his own wounds, to check on the person he was primarily responsible for," Brooks said of Scalise's security guard. "We insisted that he go back and get attended to because he was bleeding, but he was doing his job. And I tell you, those two security details, those two Capitol Police officers, they showed incredible bravery."
When asked how he plans to absorb the experience of being at the scene of the shooting, Rep. Bill Johnson of Ohio told Fox News, "It emboldens me. It tells me that we're doing what we're doing for a reason."
He added, "We don't cower in the corner from these kinds of incidences. We can't let the bad guys win."
CORRECTION: This story has been updated to correct the victim to whom Brooks applied aid.