Earlier this week, I referenced Bill James' suggestion that ground-ball pitchers are a) overrated, and b) particularly injury-prone. In the comments under Bill's original essay, longtime (and legendary) sabermetrician/historian Craig Wright chimed in to suggest that Derek Lowe wasn't handled properly by the Indians last spring. Meanwhile, we got to wondering why a ground-ball pitcher -- that is, a sinkerballer -- might be more injury-prone than another sort of pitcher.
I'm lucky enough to know Craig Wright a little, so I asked him. His response:
First, let me lay to rest any notion that sinkerballers are not working hard because they tend not to throw as fast as the average pitcher. A sinkerballer is in fact working quite hard to get the speed of his sinker up to a workable speed. There is less spin on a natural sinker and that increases the air resistance on the pitch and slows it down. This is the same principle for why a pitcher's two-seam fastball is slower than his four-seam fastball and why pitchers with stubby fingers have trouble throwing as fast as pitchers with long fingers. There is a loss of velocity there that has nothing to do with the effort in throwing the pitch, but simply results from throwing a pitch with more air resistance.
I believe the big issue with sinkerballers is that most continue to have as good or even better sinking action when their arm is a little tired. That doesn't happen with a normal fastball, which tends to lose effectiveness when the shoulder crosses the line of fatigue. As I've said many times, the key point in managing a pitcher's workload is not about pitches or innings in general, it is about curtailing the pitches and innings when the shoulder is starting to stress from fatigue. We are inclined to be more careless with a sinkerballer in that regard. He is more likely to be left in a game when his shoulder is most vulnerable to being damaged. That's the theory that I think makes the most sense.
This does make sense to me. Between working harder to keep their two-seam fastball in an effective range of speed and perhaps being encouraged to throw pitches when fatigued -- because of that perception that sinkerballers are actually more effective when fatigued -- we might expect them to suffer more fatigue-related injuries.
Of course, what we're still missing -- as far as I know, anyway -- is some data proving (for example) that pitchers who rely on two-seam fastballs are particularly injury-prone. Twenty years ago, it would have been difficult for anyone to find that sort of data. But considering that we have pitch information for the last few years and play-by-play data for the last few decades, this should actually be fairly simple for someone with decent database skills. Anybody game?