Scalise and others were practicing for an annual congressional baseball game.
Five people, including the suspect, were transported to a local hospital.
President Donald Trump said he's "deeply saddened" by the news.
A gunman opened fire on a group of Republican lawmakers practicing for a congressional baseball game at around 7 a.m. Wednesday in Alexandria, Virginia, hitting several people.
House Majority Whip Steve Scalise (R-La.), who was there braving the heat with others to practice for the annual event, was shot in the hip, his office said in a statement. He is undergoing surgery at the nearby Medstar Washington Hospital Center and is in stable condition.
Scalise was "in good spirits and spoke to his wife by phone" ahead of the surgery, his office said.
Five people, including the suspect, were transported to a local hospital, Alexandria Police Chief Michael Brown said during a press conference Wednesday. The FBI is taking over the investigation into the shooting.
Zachary Barth, a staffer for Rep. Roger Williams (R-Texas), said on Facebook that he was shot but is "okay," Yahoo's Jon Ward reported. Williams also said in a statement that one of his staffers was shot.
Two victims are being treated at George Washington University Hospital, hospital spokeswoman Susan Griffiths told HuffPost. Both are in critical condition.
Sen. Rand Paul (R-Ky.), who was also at the practice, told MSNBC that Scalise crawled through the dirt, bleeding, to get away from the shooter. Rep. Mo Brooks (R-Ala.) told reporters that he used his belt as a tourniquet to stop Scalise's bleeding at the baseball field.
Paul said that a number of aides were lying down during the attack as the shooter fired bullets their way.
Capitol Police officers at the event responded and engaged the suspect in gunfire, U.S. Capitol Police Chief Matthew R. Verderosa said. Alexandria Police responded soon after. "At that point, we were able to calm the situation and victims were transported to the hospital," Verderosa said.