We’re coming off a season in which the American League Cy Young winner had a meh fastball. It’s true. Corey Kluber‘s sinker didn’t meet the above-average benchmark for swinging strikes (5.6%, his was 5.3%) or grounders (50.5%, his was 48.6%). Look at National League breakout Tanner Roark’s two-seamer, and you’ll see the same thing. Is it possible that we’ve overrated the importance of the fastball with respect to overall outcomes?

Fastball velocity is usually the first thing on the scouting report, and with good reason. We know that every mile per hour is worth a fraction of a run allowed per nine innings. So it seems important.

I asked Steven Staudemeyer to run a correlation between the swinging strike rates on the four major pitch types and a pitcher’s overall swinging strike rate. Here is that table (all p values are less than .0001).

Obviously the fastball is important. It’s thrown nearly three-fifths of the time! The fastball’s swinging strike rate explains almost half the variance in the pitcher’s overall swinging strike rate.

But look at the slider and the change. They each explain nearly double the variance in swinging strike rate than you’d expect if you just went by volume alone. It makes intuitive sense — you use the fastball to get ahead, and you use the other pitches to finish them off — but it has all sorts of practical applications.

Take, for example, a pitcher like Dan Straily. His fastball was down below 90 mph before he was traded to the Cubs, so he had below-average velocity for a right-hander. He still managed above-average whiffs (7%), but few would say that his best asset is his four-seamer. But if you look at his change (18% whiffs) and slider (21.7% whiffs), you see that he has two pitches that break in different directions and get good results. You might take a chance on him if you thought that he could use the fastball mostly to get ahead, and if you thought the fastball was a little bit less important than it seemed by volume.

There are other names on this list, too. Ivan Nova has a nice curve (13%) and slider (23%) and an iffy four-seamer. He could switch to the sinker and have more success, even if it’s mediocre. Teammate Wade Miley doesn’t get 50% grounders with his sinker or 6% whiffs with his four-seam, but he does have a nice change (14.4%), slider (18.4%), and curve (10.5%) combo. Jerome Williams keeps getting shots despite his fastball because his change (16.5%), slider (16.7%), and cutter (10.8%) all rate as above-average by whiffs.

On the other hand, this is clearly just the first step. Each pitch is interrelated, and so there are issues with comparing these correlations. And there are probably diminishing returns on throwing off-speed pitches more, so volume is still really important. But there has to be a way to study this further. Ideas are welcome.