At the top of his game, Tom Glavine owned a reverse platoon split. His statistics would show him more effective against right-handed batters than left-handed batters, despite Tom throwing from the left side. During my time at ESPN in the 1990s, I asked both Ray Knight and Greg Olson (Glavine's former catcher) why Tom owned that split. Both gave the same answer, both calling Glavine's off-speed pitch, "a dead fish," one that moved away from right-handed batters.
Matt Harrison is showing a reverse platoon this season. In his first three years in the majors, Matt produced a normal left/right split. As you can see, his off-speed pitches to right-handers came in pretty straight, even coming a little in on righties:
This season, those pitches started moving away from the righties:
He's shutting down right-handed batters so far this season, holding them to a .135/.224/.192 slash line. He's showing righties something different, and they have yet to adjust to the change.