You Can't Hit What You Can't See

Hall of Fame pitcher Warren Spahn never studied biomechanics or captured 3D motion capture of the batters he faced, but he knew a lot about the science of strikeouts.  “Hitting is timing.  Pitching is upsetting timing,” Spahn stated decades ago. “”A pitcher needs two pitches, one they’re looking for and one to cross them up.” After all of these years, ASMI biomechanist Dave Fortenbaugh has put this theory to the test in his lab.

With less than a second to see the pitch, identify its speed and location then execute an intercepting swing of the bat, a baseball player’s margin of error can be milliseconds or millimeters.  Since most of the bat speed and power of the swing comes from the weight transfer and rotational speed of the hitter’s body, it is critical that the entire process starts at just the right time so that bat connects with the ball in the perfect horizontal and vertical planes.
Fortenbaugh, whose Ph.D. dissertation was titled “The Biomechanics of the Baseball Swing, set out to see what physically changed about a hitter’s swing when he faced pitches of different speeds.  In new research published in Sports Biomechanics, he and his team gathered 29 professional baseball players (minor league AA) to observe and record the physics of their swings.

Their focus was on a key force for any human movement known as the ground reaction force or GRF.  When you stand still, your feet create a force on the ground equal to your weight.  At the same time, following Newton’s Third Law of Motion, the ground creates an equal and opposite force on your feet, aka the GRF.  When moving, a person’s feet create not only a GRF in the vertical direction but also one horizontally.

Hitting coaches use this force to stabilize a batter’s feet while their weight is shifting from the back foot to the front foot, or from the right foot to the left foot for a right-handed batter.  Fortenbaugh hypothesized that when batters get fooled by a change in pitch speed, the timing of their step and weight shift gets thrown off causing the bat to come through at the wrong time.

For the experiment, the players were asked to face either fastballs or changeups thrown by a live pitcher.  They placed each of their feet on a force plate which measured the level and timing of the force applied as compared to the timing of the ball arriving.

Hitters are often coached to expect every pitch to be a fastball, then adjust if they see something slower.  If they don’t recognize an off-speed pitch soon enough, they will begin their biomechanical process too early, throwing off the eventual swing and contact with the ball.

What the researchers found was that the back foot force stayed roughly the same for either fastballs or changeups.  This would be expected as a player’s weight starts here.
However, for the front foot, the results were significantly different.  As Fortenbaugh concluded, “The batter applied maximum vertical and horizontal braking forces earlier for a successfully hit changeup than a successfully hit fastball, and even earlier for an unsuccessful swing against a changeup. This may be an indication that the batter is fooled a little when successfully recognizing a changeup in adequate time and fooled quite a bit more on unsuccessful swings when this recognition occurs too late.”

Because they weren’t able to identify the slower changeup earlier, they started their swing motion too soon.  For every hitter, specialized visual and cognitive training to recognize pitch types sooner would buy them the valuable milliseconds they need.

The big takeaway from all of this?  “This study provides biomechanical evidence that an effective off-speed pitch, as postulated, upsets a hitter’s timing,” states Fortenbaugh. “The data in this study also support the claim of the difficulty of hitting a baseball well, as literally just tiny fractions of a second separated the successful and unsuccessful swings.”
In other words, Spahn was right.

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