Bullets can be heard ripping through the air in the footage captured by a witness close to the field at the Eugene Simpson Stadium Park.
"We knew they were here and we knew who they were", Nathan said.
"He's behind home plate", another person responds.
Later in the video a man can be seen lying in the middle of the baseball field.
"I assume people've been calling 911 already", he says. "Is that guy shot?"
"Hey, is that guy OK out there?" the witness asks, at one point, in an apparent reference to Rep. Steve Scalise who was badly injured in the shooting. "Is anyone talking to him?"
Nathan told the New York Post that he was "more pissed off" than scared during the shooting. The alleged shooter, James Hodgkinson, 66, of Belleville, Illinois died following a shootout with authorities. He is in critical condition after undergoing surgery.