Rizzo hit a ground ball to Astros second baseman Jimmy Paredes, who made a high throw to first base that Wallace jumped in the air to try to catch. The ball whizzed over Wallace's glove and into the Astros' dugout.
Rizzo, trying to beat the throw, tangled legs with Wallace, shot up in the air and landed hard on the ground. He stayed on the ground for a few moments before walking off the field with help.
"I was really stunned and dazed at first," Rizzo said. "I think that's why I didn't move. I think I was checking out everything to make sure everything was OK. I got up and I was still stunned, but it kind of wore off. I'm now just more sore than anything."
Joe Mather pinch-ran and stayed in the game in right field. Bryan LaHair moved from right field to first base.
After the game, Rizzo said he was getting lots of text messages and phone calls wondering about his condition. His teammates weren't taking it as seriously -- several of them in the clubhouse watched the replay over and over on an IPad.
"I looked like a gymnast," Rizzo said. "I felt like [I was] catapulting a little bit. It was an ugly fall."
Manager Dale Sveum said he was glad Rizzo is OK.
"I think tomorrow, he'll probably wake up pretty darn stiff," Sveum said. "I think it'll just be a day-to-day thing."