MLB Rookie Report: Zac Curtis, LHP, Arizona Diamondbacks

This past weekend, the Arizona Diamondbacks made an unusual move, promoting rookie left-hander Zac Curtis directly to the major league roster from the High-A level, skipping him past Double-A and Triple-A entirely.  Who is this guy and why did this happen?

Basic data from the 2016 Baseball Prospect Book:

Zac Curtis, LHP, Arizona Diamondbacks
Bats: L Throws: L HT: 5-9 WT: 180 DOB: July 4, 1992

Zac Curtis was drafted in the sixth round in 2014 from Middle Tennessee State University. He dominated as a starter in college and he’s dominated out of the bullpen in pro ball, firing strikes with a 90 MPH fastball, an above-average slider, and a workable curveball and change-up. He has a starter’s arsenal but his small stature makes him better-suited to bullpen work in pro ball. So far he’s been excellent. He controls right-handers as well as lefties so it may be possible for him to move beyond LOOGY work into a firm middle relief role if he continues this at higher levels. Grade C.

ADDITIONAL COMMENTARY

Curtis was stellar last year in the Low-A Midwest League, posting a 1.33 ERA in 54 innings with a 75/12 K/BB, just 33 hits allowed, and 33 saves in 36 opportunities for Kane County. Pitching this season for Visalia in the California League, Curtis has a 5.23 ERA in 10.1 innings, giving up 11 hits, but with a very high strikeout rate at 22 whiffs against five walks. He reportedly impressed Diamondbacks brass in spring training and they looked past the high-but-small-sample ERA this year, focusing on the strikeouts.

As noted, Curtis doesn't profile as a typical two-pitch reliever: he has a full four-pitch arsenal and he knows how to use it. racking up strikeouts at an elevated pace. His platoon splits are close enough that he may not be confined to LOOGY work: if his command holds up he can get right-handers as well as lefties out. The risk here is that he hasn't tried out his approach against advanced hitters in the high minors, let alone in the majors, and has only a handful of High-A innings under his belt. They are asking him to learn on the job with little experience to fall back on.

I would not under-estimate Curtis or assume that he's doomed to struggle due to his lack of upper minors experience; his makeup is reputedly very strong and he has an aggressive, fear-no-hitters approach. This will be an interesting experiment to watch.