The injury occurred in the bottom of the second inning. With Atlanta leading, 4-0, Freddie Freeman swung at a 2-1 pitch from right-hander Stephen Strasburg and hit a long drive to right field. Souza chased after the ball and collided with the wall at full speed as the ball went over the fence for a two-run homer.
Souza was on the ground for at least a minute, while Williams, athletic trainer Lee Kuntz and several teammates came to his aide.
Souza saw the video of the collision and was surprised that he wasn't seriously injured. He said the pad on top of the right-field wall prevented him from sustaining a head injury.
"There isn't much damage," Souza said. "I just think the impact of being stopped at full speed is kind of where we are at. It hit my shoulder and neck right there."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.