Zack Greinke on Curveballs by Eno Sarris April 23, 2014 Earlier in the week, we talked about the evolution of Zack Greinke’s pitches. Mostly the piece was about the dalliance of his slider and his cutter over his career. Left on the cutting room floor was a mini conversation we had about his curveball. It didn’t fit the narrative because it wasn’t about an adjustment he’d made. But what he said did send me on a journey through the numbers. Turns out, Greinke’s curve — despite being his third-best pitch and owning average peripherals — improves when compared to its true peers. First, what the pitcher said about curves generally and his in particular. He thought the pitch wasn’t great for whiffs in general because batters recognize it and “you don’t get many swings.” The curveball gets the lowest swing percentage in baseball. But trying to get called strikes on the curve is problematic, too. “My curve is so slow, that they might say ball, and if not, they can still react to it,” Greinke said. “[Justin] Verlander’s is so sharp that by the time they realize it’s a strike, they can’t swing at it.” To some extent, the pitcher was right — the fastest 30 regularly-thrown curve balls last year had a 20% called strike percentage, while the slowest thirty only showed a 17% number (Greinke’s came in at 16.7%). Not a big difference, though. He felt the pitch was a good change of pace because it was a slow curve — it averages just over 70 mph these days — and it caused the batter to be out in front of the pitch. But he wasn’t sure if that was why curves turn into grounders. “The number one thing for curves and grounders — they are low in the zone,” said Greinke of the pairing. All low pitches turn into grounders more, but it’s particularly true of curve balls, but not in the way it may first seem. 48.7% of all curves get grounders. Curve balls in the bottom third of the zone (and a little below) get grounders 48.2% of the time. But almost half the total curve balls land in that bottom third, so it’s hard to separate out the effect from the fact that most curves show up there. One thing that becomes obvious is that velocity helps curve balls as much as it helps other pitches. Take a look at how the regularly-thrown fast and slow curve balls from starters fared in 2013: Velocity GB% swSTR% Sample 76.9 0.474 0.112 Fast CB 81.5 0.494 0.141 Slow CB 72.0 0.438 0.110 Top-50 GB% 77.8 Top-50 swSTR% 78.3 If you look at Greinke’s curve ball among the population of curve balls, it’s not super impressive. At 10% swinging strikes and 50% ground balls, it’s almost perfectly average — 11% swinging strikes and 49% ground balls is average among all curves. But if you look at Greinke’s curve compared to the other slow curves, it starts to stand out. The pitch may be his worst off-speed pitch, but that’s only because he’s got a wicked slider and an improving change-up. And really, his change-up is the newest kid on the block. When seen over his career, Greinke’s change may be slow, but it’s more effective than the average slow curve ball.