On August 22, 2000, the Colorado Rockies sent Brent Mayne in as a relief pitcher in the 12th inning against the Atlanta Braves. Mayne, the Rockies’ regular catcher, was unable to swing a bat due to a sprained left wrist and had missed the previous four games. Out of pitchers, manager Buddy Bell asked Mayne if he could pitch. Mayne, who later said he had never pitched at any level, responded, “Yeah, I can pitch.” He pitched one inning, surrendering no runs with a fastball that topped out at 83 miles per hour. Colorado won the game the next inning when rookie Adam Melhuse, pinch-hitting for Mayne, singled with the bases loaded and two outs. Mayne thus became the first position player to be credited with a win since 1968.
You can read more about Brent Mayne here.