Earlier this week, the Cardinals called up a promising young arm in Alex Reyes, who’s already enjoyed some success out of St. Louis’ bullpen. Another promising young arm is set to debut for the Cardinals tomorrow, as 22-year-old Luke Weaver will get the start against Cubs. What should we expect from him?

One thing we know for certain is that Weaver was undeniably excellent in the minors this year. In 13 starts this year — most of them at Double-A — he pitched to a sparkling 1.30 ERA and 2.11 FIP. He struck out an impressive 28% of opposing batters, while walking fewer than 4%, which is equally impressive. It wasn’t the first time he tasted success either, as he pitched well last season in High-A, albeit with a more underwhelming 21% strikeout rate.



My KATOH projection system projects Weaver for 4.9 WAR over his first six seasons by the traditional method and 5.1 WAR by the method that integrates Baseball America’s rankings. Weaver placed 75th and 71st overall, respectively, on KATOH’s recent top-100 lists. Among pitchers, though, he was 14th and 18th, respectively. That’s not as good as his teammate, Reyes, who clocks in at third and first, but it’s still pretty good. On the traditional KATOH 100, Weaver slots in directly behind Lucas Giolito, whom I think you might have heard of. Also, as you may know, KATOH’s lists tend to be relatively hitter-heavy — likely due to some combination of pitchers’ attrition rates and the fact that KATOH does not directly quantify “stuff.” So the fact that Weaver is among the top 20 of pitching prospects via KATOH is certainly notable.

To help you visualize what his KATOH projection entails, here is a probability density function showing KATOH+’s projected distribution of outcomes for Reyes’ first six seasons in the major leagues.

To put some faces to Weaver’s statistical profile, let’s generate some statistical comps for the commanding righty. I calculated a Mahalanobis distance between Weaver’s 2016 performance and every Double-A and Triple-A season since 1991 in which a pitcher recorded at least 350 batters faced. In the table below, you’ll find the 10 most similar seasons, ranked from most to least similar. The WAR totals refer to each player’s first six seasons in the major leagues. A lower “Mah Dist” reading indicates a closer comp.

Please note that the Mahalanobis analysis is separate from KATOH. KATOH relies on macro-level trends, rather than comps. The fates of a few statistically similar players shouldn’t be used to draw sweeping conclusions about a prospect’s future. For this reason, I recommend using a player’s KATOH forecast to assess his future potential. The comps give us some interesting names that sometimes feel spot-on, but they’re mostly just there for fun.

Weaver is somewhat unproven, especially for a 23-year-old who’s cracking top 100 lists. He doesn’t have a terribly long track record above A-Ball, and has barely pitched at all above Double-A. But he’s risen to every challenge he’s faced thus far, and has pitched about as well as you can reasonably expect someone to pitch.

Weaver is a different breed than his teammate Alex Reyes. While Reyes does it with flashy stuff, crazy strikeout numbers and lots of walks, Weaver does it with good stuff, good strikeout numbers and very few walks. Weaver’s long-term outlook isn’t as promising as Reyes’, but that’s no slight to Weaver. By my math, he’s still one of the 20 best pitching prospects in baseball.