A 17th-round draft pick out of Clemson in 2015, Koerner has worked his way up the Yankees’ system fairly quickly, and he was recently promoted to Trenton on July 3, and I was able to see his start on August 6, where he worked 5 1/3 innings in a extra-inning loss to the Altoona Curve, giving up six hits, walking one, and striking out two.
Koerner brings sound mechanics and a free and easy arm action, and average arm speed from a 3/4’s arm slot. He repeats well, and it shows in his overall plus control numbers of 1.3 and 2.3 BB/9 over his past two seasons. While he has a four-pitch mix, Koerner lives in the lower third of the zone throwing mostly sinkers sitting 88-to-91 mph with fringy dive and below-average command in the zone, and the fringe average life he gets leaves him with a 45-grade heater overall. He’ll also throw the occasional two-seamer in the 91-to-93 mph range, and a changeup in the 78-to-80 mph range that was also used sparingly. He showed some feel for spin on his breaking pitches, and he used a few for first-pitch strikes the second time through the lineup. He has feel to change shapes, ranging the looks from an 11-to-5 shaped fringy curveball that had gradual break in the 75-to-78 mph range, to an average slider with ¾’s depth and limited bite in the 82-to-85 mph range.
Despite plus control, Koerner’s command of his arsenal is below average overall, and he lacks a true out pitch at present. He’s susceptible to contact when working from behind (all six of his hits allowed in this outing were from even or behind in the count) and needs a strike. While the control numbers have been consistently plus or better in his pro career, he is working with razor thin margins in the zone, and has to work from ahead to be effective. His contact rate has risen to 10.8 H/9 over his 41 2/3 Double-A innings versus 7.9 H/9 over 36 2/3 innings in Tampa, while his GO:AO ratio has been cut in half from 2.40 in Tampa to 1.13 at Trenton, and his strikeout rate has dropped from an average 7.7 SO/9 last year to a below average 5.7 SO/9 this season. He is likely high-risk, Role 35 up-down emergency arm capable a middle relief or spot-start role if the sinker and slider command can reach average.