The freak accident happened as Colvin was running the bases in the second inning. Catcher Welington Castillo's bat broke as he was hitting a double to left field.
Colvin looked around from near third base to see where the ball was going and Castillo took off running. Neither one of them realized what was about to happen.
When Colvin saw the ball was going to be a hit, he turned just in time to feel the sharp edge of a bat piercing his chest. He still scored and apparently tried to shrug it off.
"I thought he was fine," pitcher Jeff Samardzija said. "We were kind of joking around; I saw a little something on his shirt. I said, 'Hey, man, maybe you better get inside.'"
A team spokesman said Colvin suffered minimal external bleeding, though the depth of the wound was not immediately clear.
The incident left some Cubs pretty upset with the maple bat that was used by Castillo and is popular among players.
"That's the danger of a maple bat," Jeff Baker said. "I saw an umpire get slashed ... in Kansas City. It's just not worth it to me to use that kind of bat. I don't want that on my conscience."
Manager Mike Quade, who didn't realize Colvin was hurt until well after the incident, was just as outspoken.
"I'm amazed it doesn't happen more often," Quade said. "Over the last 10 years, I've seen a lot of projectiles out there. Sometimes I've seen it happen three or four times a night where bats get snapped in half. Years ago, I don't remember that happening that often."
Castillo said he has used maple bats "my whole life."
But the catcher felt terrible for Colvin, who was his teammate in the Minors for three years.
"I just hope he comes out of this OK," Castillo said.
Quade speculated that Colvin's physique could play a role in overcoming this bizarre injury.
"He's such a strong guy in the upper body," the manager said. "Maybe that helped him."