In addition to calling up stud center-field prospect Lewis Brinson, Milwaukee also recently summoned talented lefty and KATOH crush Josh Hader. Although Hader’s worked primarily as starter in the minors, the Brewers plan to use him out of the bullpen for the time being. A 19th-round pick out of high school, Hader’s been exceeding expectations for years. He owns a 3.87 FIP and 27% strikeout rate in 541 minor-league innings. In 25 starts between Double-A and Triple-A last year, he pitched to a sparkling 3.07 FIP with a 31% strikeout rate.

Things didn’t go as swimmingly for Hader in Triple-A this year, however. He maintained a solid 22% strikeout rate, but matched it with a 14% walk rate and coughed up an uncharacteristic 14 homers in 52 innings. The end result was a 5.37 ERA and 4.93 xFIP, which doesn’t exactly scream “big-league ready.”

Still, KATOH remains optimistic. My system projects Hader for 5.0 WAR over his first six seasons by the traditional method and 5.7 WAR by KATOH+, which incorporates scouting rankings. That makes him one of the top 10 pitching prospects in the minors, and a mid-top-100 guy overall.

To put some faces to Hader’s statistical profile, let’s generate some statistical comps for the 6-foot-3 lefty. I calculated a weighted Mahalanobis distance between Hader’s Double-A and Triple-A performance and every season since 1991. 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.

Despite his relative lack of prospect pedigree, Hader’s stuff is almost certainly of big-league quality. The lefty’s fastball averaged over 94 mph in his debut, and both his slider and changeup project to plus according to Eric Longenhagen. However, scouts have long contended that Hader profiles best as a reliever. To wit:

• Eric Longenhagen, 2017: “Those who consider him a reliever cite the rarity of a delivery like this in starting rotations across baseball, the potential platoon issues Hader might face as a low-slot lefty, and his fringey control.”
• Baseball America Prospect Handbook, 2016: “His reliance on his outstanding fastball combined with just ordinary control make him a possible bullpen candidate.”
• Baseball America Prospect Handbook, 2015: “Durability will always be a question because of Hader’s size and how he slings the ball across his body… His reliance on his fastball profiles him better as a reliever.”
• Baseball America Prospect Handbook, 2014: “It’s one of the most unconventional deliveries a starter could use… Scouts see him as a future lefty reliever where his low arm angle will make life difficult for lefthanders.”

Despite the persistent “future reliever” label, Hader dominated for years as a starter in the minors. But when he finally sputtered in Triple-A, the Brewers seemingly decided to try him in the pen. Given his stuff and minor-league performance, I have little doubt that he’ll be a dominant force there.