In baseball, we frequently use the term ‘motor preference’ to refer to an athlete’s natural movement patterns—his default setting, if you will. No two human bodies are the same, which means no two pitchers will move in the same exact way. You can see this with basic pitching mechanics; there are a wide variety of ways to throw 95 mph, for example, and each high-level athlete arrives at that destination in a unique way that fits what their body is naturally good at. And as pitcher training becomes more of an individualized process, understanding each hurler’s strengths and weaknesses is at the very core of successful player development.
As it pertains to the scope of this piece, we’re looking at movement bias in the sense of how a pitcher tends to apply pressure to the ball at release. There are lots of factors that play into this, from how a pitcher’s limbs are built to his mechanics, and the spectrum of motor preference is very wide in this regard. But for simplicity’s sake, we’re going to divide these preferences into three categories: supination bias, backspin bias, and our main topic for today; pronation bias.
Motor Preferences
In simple terms, pronation bias is the tendency to get on the inside part of the baseball at pitch release. Backspin bias is what I personally call the tendency to stay behind/through the ball, and supination bias applies to being on the outside of the ball. Each of these three categories leads to really drastic differences in the kind of pitch movement a pitcher is naturally good at imparting on the baseball. With the disclaimer that most pitchers tend to fall somewhere in between the extremes, let’s put each motor preference in context and see what kind of pitch mix it lends itself to.
Supination Bias
Supination-dominant pitchers are often breaking-ball masters. Their natural tendency to get on the outside of the ball means they usually have an easier time putting all sorts of spin on it. It’s common for these guys to cut their fastball as well, leading to a pitch mix dominated by glove-side movement. In contrast, they can struggle to pronate and lack the ability to create arm-side run, sometimes leading to poor shape on traditional changeups. Supinators are almost always candidates for seam-shifted wake, most often applied to sinkers, changeups, and sliders. You can likely picture this kind of pitcher with ease: Corbin Burnes, Kyle Bradish, etc.
Backspin Bias
Backspin-dominant pitchers are the kings of the rising fastball. Their natural tendency to stay behind the baseball allows them to impart efficient backspin on the ball, creating elite vertical movement on a four-seamer. They often have access to the full array of breaking balls, but can sometimes run into issues with their changeups. Because they stay behind the ball to such a degree, it can be difficult for them to remove backspin from their cambio, leading to floating changeups without impact dive. This is part of why splitters are often such good fits for pitchers of this kind, as their low-spin nature allows them to kill that vertical movement. Logan Gilbert and Justin Verlander are two good examples of this kind of hurler.
Both supinators and backspin-dominant pitchers are instinctive profiles to understand. On top of that, both of these variations often feature eye-popping metrics for pitches we all associate with modern strategy: high-spin breaking balls or high-carry four-seamers. But pronators are different.
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