Jhoulys Chacin hasn’t thrown a curve ball yet this season. Don’t think he hasn’t noticed. “That was my strikeout pitch,” he said, while agreeing he hasn’t thrown it. But he used it more before the four-man rotation, before the team decided to emphasize ground balls, before he injured his pectoral muscle, and before he learned the benefits of contact. This year, he hasn’t thrown a curve ball.

The curve ball thing has been going on for a while. He threw the pitch 15.6% of the time in his debut and then that whittled away gradually to 6.7% last season. His strikeout rate fell from over 20% (and above average) to 14.3% last year, too. But as he threw the pitch less, he got more ground balls, too. At least until last year.

Last year, the Rockies tried a four-man rotation with a 75-pitch limit. “I really didn’t like it,” Chacin admitted. The 75 pitch limit was strict, and it was hard for the pitchers to compete with that number hanging over their heads. “But I learned,” said Chacin, “I learned that you have to pitch to contact, too.”

With a hard ceiling of 75 pitches, Chacin had to simplify. “Even with two strikes, I had to focus on getting a ground ball,” he said. “I have to get it done,” he remembers thinking. He couldn’t afford to keep trying to get the whiff. You had to go after the hitters and get “quick outs.” So now it’s the fastball, the sinker, the slider and the changeup. Everything down.

He’s cut pitches from his plate appearances with the approach. The first two years in the big leagues, he averaged 3.99 pitches per batter. Since, he’s whittled that number down to 3.77. Over the course of a full season, that could make a difference. Face 800 batters, and you’d save 176 pitches, for example. Every pitch counts.

But the curve ball can get grounders, too, if you throw it low, and Chacin took care to point that out. The biggest predictor of batted ball trajectory is location, and he was well aware of that fact. Dave Allen once produced a very simple graph that depicted the situation:

If he’s throwing the curve ball — his erstwhile strikeout pitch — less often, but not necessarily because of the team’s emphasis on the ground ball, or because of something that happened while they were experimenting with the four-man rotation… why is he throwing the curve ball less often?

“It’s hard to throw a curveball in Colorado,” said Chacin. He likes to throw more sliders in Colorado. It’s hard to get that break, that bite in the dry, thin air, perhaps. Here, in San Francisco, Chacin said “you can throw your breaking ball and get the strikeouts.” But in the mountains? “Just throw a ground ball, whatever, get the out,” he said.

Chacin is not alone in avoiding the curve in Colorado. Take a look at all pitch types everywhere, and then the pitch types in Colorado, courtesy Jeff Zimmerman:

Type Non-CO CO only Change 11.00% 9.80% Curve 9.40% 8.10% Cutter 5.40% 5.00% Four Seam 36.60% 42.70% Split 1.20% 1.40% Two Seam 11.10% 6.40% Sinker 9.20% 7.50% Slider 15.30% 18.50%

The story of Jhoulys Chacin is the story of the everypitcher, it seems. The curve actually suffers the most, when it comes to pitch selection in Denver, a finding that Dan Rozenson recently described and explained — the atmosphere robs the pitch of much of its effectiveness. Pitchers throw more four-seamers and sliders in the thin air, and the slider had the most comparative advantage in Rozenson’s study.

Jhoulys Chacin seems to have figured out how to pitch for his team. They’re lucky to have him for two more years, but even after that time is over, teams should remember — now he knows how to pitch both ways: “I’ve still got my curveball.”