The veteran right-hander ran to cover home plate after a wild pitch as the Diamondbacks' Eric Chavez came home from third. The throw from catcher Wilin Rosario sailed past Oswalt, who immediately indicated he was hurt.
Oswalt had difficulty walking as he was accompanied into the Colorado dugout. Right-hander Edgmer Escalona came on in relief.
"I never had a hamstring pull in my life. I don't know the timetable on it," Oswalt said. "I felt it when I was trying to slow down. They got it so wet around the plate I kind of slipped. I was trying to change direction a bit. He threw the ball up a little bit. I don't really know exactly when it popped. I just felt it pop and knew right away that there was no way I was going to be able to go back on the mound."
Oswalt allowed 1 earned run and two hits and fell to 0-4 in his first season with the Rockies.
Information from The Associated Press was used in this report.