This happened in Washington State in a HS playoff game a few years ago. Pitcher switched arms, batter switched boxes and back forth they went until the umpire stopped play and made them choose. This led to a rule change in Washington permitting one change per batter/hitter per inning. The pitcher was Drew Vettleson, a rising prospect in the Tampa Rays system (OF). He was a fine HS pitcher and threw both right and left.