Brooks told CNN that gunman was behind the dugout when he opened fire. He said the suspect was shot by members of the congressional protective detail.
Scalese, after being hit, dragged himself across the field in an attempt to get to cover, Brooks said.
Brooks added that he saw Rep. Gary Palmer being treated at the scene.
As the third-highest ranking House Republican, Scalise has a round-the-clock Capitol Police detail.
Brooks told CNN that without the Capitol Police, “We would have been at the mercy of this shooter, and he had a lot of ammo.”
He added that without the police, “all we would have had was a baseball bat versus a rifle. Those aren’t very good odds.”
Sen. Rand Paul, Sen. Jeff Flake and Rep. Chuck Fleischmann were present when the shots rang out and Paul told ABC that Capitol Hill police fired at the suspect.
Paul said he heard the shots from right field and hid behind a tree before running toward a fence. He recalled bullets hitting the ground around him, he said. Paul told ABC that he hopped a fence to escape.
A witness tweeted that at least three of the politicians had taken shelter in his home amid the attack.
Another man shared a photo of a cracked window with a bullet hole, writing, “Active shooter situation during this mornings trip to the Y. Terrifying. Am ok. Sheltered in place & under lockdown.”
In a statement the White House said that Donald Trump and Vice President Mike Pence are aware of the shooting.
“We are deeply saddened by this tragedy,” the statement read. “Our thoughts and prayers are with the members of Congress, their staffs, Capitol police, first responders, and all others affected.”