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Zack Godley vs. Matt Koch: a comparison

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In 2017, an unheralded starter emerged from Arizona’s farm system when we needed him most. Is the same thing happening in 2018?

Los Angeles Dodgers v Arizona Diamondbacks Photo by Christian Petersen/Getty Images

It’s quite remarkable the parallels between the rises to prominence of Zack Godley and Matt Koch. In April 2017, the largely unknown 27-year-old Godley, who had made some spot appearances over the previous two years, was pulled into the rotation when Shelby Miller needed Tommy John surgery, and became a mainstay of Arizona’s pitching staff. In April 2018, the largely unknown 27-year-old Koch, who had made some spot appearances over the previous two years, was pulled into the rotation when Taijuan Walker needed Tommy John surgery, The parallels have been noticed by many:

But will he continue to follow suite, and also become a mainstay of Arizona’s pitching staff? There are grounds for concern, as BenSharp highlighted in this morning’s Snake Bytes: “His peripherals worry me. He has 4.42 FIP due to a low strikeouts and mediocre walk avoidance. He is mostly producing based on a .214 BABIP and a 87.7% LOB%. He has a good groundball rate, but not great and he’s being hit hard. I looked him up in statcast to see if he was allowing weak contact or something, but has an average exit velocity of 90.9 MPH, which is 19th worst in the league. In fact his xwOBA is .370, which is way higher than the .277wOBA he’s currently producing. All of this seems to point to heavy regression going forward.”

However, Ben offered an escape clause: “Hopefully he improves his peripherals instead.” And, it’s worth noting, that’s exactly what Zack Godley did. We can compare the two pitcher’s first 25-odd innings, from this year and last.

Godley vs. Koch

Pitcher IP H R ER BB SO HR ERA BA OBP SLG OPS BAbip
Pitcher IP H R ER BB SO HR ERA BA OBP SLG OPS BAbip
Godley 25.2 17 7 7 10 20 2 2.45 .195 .278 .310 .589 .231
Koch 25.1 18 7 6 7 17 3 2.13 .200 .273 .378 .651 .214

Both pitchers had a mediocre K:BB ratio, and benefited from a low batting average on balls in play, which helped suppress their early ERAs. Godley did regress somewhat, with a 3.55 ERA the rest of the way - but also improved his K:BB ratio, from the 2.00 figure in the early going, to 3.37. He did that on both ends, cutting down the number of walks, and striking out better than a batter per inning, as his filthy curveball became Zack’s weapon of choice. Does Koch have that potential? The problem might be that his minor-league stats are considerably less impressive than Godley’s. Neither logged much time at AAA - 60 IP for Godley, less than a hundred for Koch - so let’s use their entire time in the minors.

	ERA  IP      H   R  ER HR  BB  SO
Godley	2.96 291.2 255 123  96 15 101 293
Koch 	4.54 505.0 589 277 255 43  97 320

You can see that Godley has the much better ERA, and this is backed up with a far better K-rate, again more than a batter per inning. Koch’s main strength on the farm was his good control, resulting in a low walk-rate, and that’s perhaps his best shot at improving the peripherals going forward in the majors. So far, his walk-rate at the major-league level has been about 50% above what it was (2.5 per nine IP vs. 1.7). Unless he’s going to develop a strikeout pitch like Godley’s insane curve, then he needs to make sure the greater number of balls in play he allows, are mitigated by minimizing the free passes.

There is one other area where Koch does seem to have changed his game-plan this year. He’s dialing up a much higher rate of ground-balls, and this has certainly saved his skin on a number of occasions - not least in the sixth inning yesterday, after a lead-off triple was followed by a hit batter. Small sample size applies, but his GO/AO rate in the majors this year (1.68) is more than double the 0.83 it was in 2016 (he didn’t get any outs in 2017...). Koch change-up appears to be particularly strong of late in this area, and we can hope this becomes as effective a weapon for him, as the curve has become for Godley. Indeed, Koch’s curve has also improved.

But there’s something else which helps explain Koch’s success, noticed by Bernie Pleskoff yesterday: “Both Koch and Verlander are putting on a clinic today about mixing up a repertoire and not just relying upon the fastball.” That’s undeniably part of the equation as far as successful pitching goes: you need to pitch away from your opponent’s strengths, as much as to your own, especially against a team who feast on the fastball, like the Astros. If you pitch smarter, then you don’t need to pitch harder, as Zack Greinke’s efforts to counter his declining velocity. It’ll be interesting to see if Koch can continue to develop; so far, he’s been a godsend to a rotation whose depth was sorely tested in the first month.