|Brian Duensing has made 50 starts and 59 relief appearances|
for the Twins during the past three seasons.
That's taking the platoon advantage to extremes.
That massive platoon split has many thinking that Duensing would be better suited to bullpen work, and that was, at one point, the Twins' idea with him. But he fared well in the starting rotation in 2009 and 2010.
What went so horribly sour for him in 2011? My guess is that he lost his change-up.
The platoon advantage is rooted in pitch movement. A left-hander's breaking balls — curves and sliders — move in on a right-handed hitter, away from a left-handed hitter. (A right-hander's, obviously, move in the opposite direction.) These are pitches that leave the hand coming between the thumb and forefinger.
Change-ups — and in particular the circle change, a favorite of the Twins organization — generally move in the opposite direction. The circle change is thrown with the thumb and forefinger curled together and with the twist for the forearm so that the ball is coming out of the hand on the side of the little finger. This gives it a reverse curve, or screwball, effect. (Indeed, Warren Spahn's description of how he threw his famous screwball sounded much like the circle change.)
Many lefties with noted change-ups — such as Johan Santana and Tom Glavine — have a tendency for reverse platoon splits. Part of it, no doubt, is that teams tend to sit their marginal left-handed hitters against quality lefty starters, but part of it is that their change-ups move down and in to left-handed hitters, and that is, as a general rule, their butter zone. These pitchers try to get lefties out with fastballs and breaking balls, right-handers with fastballs and change-ups.
That Duesning is effective against lefties suggests that he has a good breaking ball; his struggles with righties, which was much worse in 2011 than in the previous season, suggest that his change-up was ineffective. Fix that, I think, and he could still be an useful member of the starting rotation — and that is much more valuable than a LOOGY.