Glove-Side Movement Overload + Impact on Pitcher's Performance

For a quick overview on what lead to this post, read my last blog about the impact of different pitch types on a hitter's timing: https://sites.google.com/view/wgentzbaseball/home/impact-of-pitch-type-on-a-hitters-timing

After my last blog post, I wanted to look more into how pitcher's who have more glove-side movement pitches perform as well as the overall impact on a hitter's timing. Going through all 2024 Trackman data, I split the data into two groups; pitchers who had been tagged using a cutter, a slider, and a curveball and pitchers who had used at least one of those pitches. During the 2024 season, there were 386 pitchers that use all three and roughly 5,800 pitchers that used at least one of those three. 

Looking at both groups' average movement profiles, there isn't any real difference between the two groups. To describe the movement profile, the CT had glove-side movement with some carry, a sweepier slider, and a curveball with ~8-9 inches of depth and some lateral movement (slightly more slurvy rather than 12-6). 

Testing Siginficant Difference in Timing

After splitting the data into groups, I tested the timing metrics on balls in play between the two groups on glove-side moving pitches as a whole. Using a two-sample t-test on R, the p-value was less that 2.2e-16, meaning there was a significant difference in timing on CT/SL/CUs between the two groups. After this, I ran t-tests on the individual pitches between the two groups. Again, the t-test showed significant differences in timing between the two groups on sliders and curveballs, however there was NOT a significant difference in a hitter's timing on cutters between the two groups. Looking at the average timings, the "NoGlove" group (pitchers who threw one/two of the three pitches) had timing father away from the "danger zone" of -5ms to -15ms by about half a millisecond with sliders and curveballs compared to the "Glove" group (pitchers who threw all three pitches). This means that the "NoGlove" group was able to get hitters to make contact a half millisecond sooner than the "Glove" group and got them more out in front.

Looking at the confidence intervals of the t-tests, it could be said that the true difference in timing on sliders curveball between the two groups could be up to one millisecond. This difference could lead to a hitter making contact with the ball roughly two inches father away from the plate and mess with his timing, exit velocity, and launch angle.

Metric Comparison

After looking at the impact of timing, the next thing to look is the performance metrics between the two groups of all three pitch types: 

Quick Notes

• Pitchers in "Glove" group have a higher Sw% (SL Sw% is 6% higher), lower BABIP (by 15-20 points) than "NoGlove" group

  • Slight differences in Whiff%, HH%, exit velocity

• Increased Chase% in "Glove" group compared to "NoGlove"

  • Statistically significant difference in Chase% between the two groups on sliders and curveballs

My assumption would be that because pitchers in the "Glove" group had more success with their breaking balls is due to the changes in velocity as well as being able to tunnel or mix those three pitches in a way to continue to keep hitters off balance. Normally the first thing a hitter notices out of the pitcher's hand is the shape of the pitch so if the hitter sees glove-side movement, he now needs to look for depth AND velocity. With pitchers in the "NoGlove" group, the hitter would see glove-side movement and either have to look for depth OR velocity. The added decision-making adds another layer of deception for a pitcher who throws all three pitches.

How to Use This

As a coach, there's a couple different ways to use this information:

For a pitcher who throws all three pitches already (or even a four-seam fastball with more cutter-like movement), my suggestions would be to have a higher usage of breaking balls and use the cutter to keep them off balance. With the increased Swing% and Chase% along with the lower BABIP, both breaking balls should play better than expect while the cutter is basically a show-me pitch to show some velocity to the hitter.

For a pitcher who throws either a combination of cutter/slider or cutter/curveball, I would suggest to the player the exact opposite. Live off of your cutter and throw the slider/curveball as a putaway pitch with two strikes or to mess with the timing of a hitter. I would avoid adding the other breaking ball UNLESS...

• The pitcher's breaking ball is struggling AND

• The pitcher's cutter usage is lower OR the cutter is his primary FB and has shown average/below average performance metrics with it

In this situation, the pitcher may sacrifice some performance on his cutter to help both breaking balls be successful and maybe help decrease the pitcher's BABIP on his cutter while increase Swing% and Chase%.