Prospect Scouting & Stats — Pitcher Pitch Grades & Strikeout Rate

After concluding our look at hitter prospect scouting grades and stats, it’s time to flip on over to pitchers. I’ll begin by looking at the pitch type grades, strikeout rates, and SwStk% marks. First, let’s see how these pitch grades correlate with those two metrics.

I calculated correlations between all the pitch grades, as well as the command grade, with strikeout rate and SwStk%. Since there were some prospect with tiny sample sizes, I required a minimum of 50 batters faced in 2019, which gave me a total population of 397 pitchers. However, not all of these pitchers received grades, and obviously every pitcher doesn’t throw every pitch, so the number of pitchers in each pitch correlation calculation is different, but all over 200. I was curious to find out whether any particular pitch grade correlated more strongly with strikeout rate or SwStk%. I was also curious if the pitch grades correlated better with strikeout rate or SwStk%. Let’s find out.

Before sharing the pitch grade correlations, the correlation between strikeout rate and SwStk% in this population was 0.39, which is surprisingly low. This compares to a correlation of 0.78 among Major Leaguers over the past five seasons (3,016 pitcher seasons of at least 50 total batters faced). I guess what this suggests is there are far more looking strikeouts in the minors than Majors.

These are not high correlations at all. I would have loved to create a linear regression equation using the grades to predict strikeout rate, but with every pitcher owning a different pitch mix, it’s beyond my skills.

Let’s now sort each column by correlation to more easily visualize which grades correlate best.

So after all we’ve heard that it’s vital to have a good fastball in the minors and everything works off the fastball, sure enough, it easily correlates most strongly with strikeout rate among all four pitch types. Still, 0.35 isn’t very high, so it takes much more than just an excellent fastball.

The most strongly correlated secondary pitch is the slider, which makes sense as it generally results in the highest whiff rate among the three pitches graded. The curve ball comes in just behind the slider.

Shockingly, the changeup grade is almost useless in predicting strikeout rate. This makes sense, as three years ago, I shared my research and linked to Eno Sarris’ research on data suggesting that changeups have a strikeout problem. Perhaps changeups have other benefits, like perhaps in reducing BABIP (I don’t know, just throwing one possibility out there), but if you’re speculating on a prospect’s strikeout rate potential, it seems safe to completely ignore his CH grades.

I threw in the CMD, or command, grade just for the heck of it, and it’s funny to see it correlative negatively with strikeout rate. Better command = worse strikeout rate? I guess because it’s easier to make minor league hitters chase a nasty pitch that ends up being a ball, so throwing fewer strikes could actually improve strikeout rate. I doubt this is the case in the Majors as well.

Okay, this table makes little sense to me. How do nearly all the pitch grades correlate negatively with SwStk%?! Seems to me based on these correlations that we shouldn’t bother trying to predict SwStk% using pitch grades. Stick to strikeout rate.

So bottom line is you want to see a strong fastball from the pitching prospect you’re analyzing. To go along with the fastball, the hope is he doesn’t rely on a changeup for his primary secondary pitch. If he throws a slider as his primary secondary pitch, that’s ideal for his strikeout rate. Adding a curve ball as well will not only benefit his strikeout rate, but also help him fend off opposite-handed batters.