There have been mixed feelings about Kohl Stewart this season. Some cite his low ERA as evidence that he has been excellent, while other point out his low K-rate and claim that he is struggling. Let’s take a closer look to see which is the case.

A Closer Look

The first thing we must consider is Stewart’s age. A prospect’s performance should never be viewed independently of their age: if a player is old for their level, they should be expected to perform well; conversely, if a player is young for their level, expectations are lower. Kohl Stewart is 19 and is pitching in Single-A. Let’s put that in perspective: he is 3 years younger than the average pitcher in his league; last year, Jose Berrios was 19 in Single-A, and was (I believe) the youngest pitcher in the league for most of the season; Kohl Stewart is currently the youngest pitcher in the Midwest League. Bottom line, Kohl Stewart is really, really young. As a result, we shouldn’t expect him to dominate. This means that if Stewart is in fact struggling, we shouldn’t worry too much; he can repeat Single-A next year and still be one of the younger pitchers in the league. Furthermore, if Stewart is performing well, we should be much more excited¹.

Now let’s take a look at his numbers: 2.58 ERA (4^th in the league), 1.15 WHIP. You’ve probably seen these numbers. They are very good. One major reason for his dominance is a .268 BABIP (well below the league average of .312). This low BABIP could be a result of poorly hit balls (a good thing) or it could be luck (not so good). However, I have no information on this. So let’s look a little deeper at the three areas I look at most with young pitchers: strikeout rate, walk rate, and ground ball rate.

As many have noted, Stewart is struggling to strike batters out; he is striking out batters in 17.2% of plate appearances (6.46 K/9), 18% below the league average of 20.3% (7.9 K/9). However, Stewart’s control has been very good: he is walking batters in 7.2% of plate appearances (2.39 BB/9), 19% below the league average rate of 8.6% (3.3 BB/9). This low-walk rate has balanced out his lack of strikeouts, allowing Stewart to post a slightly above league-average K/BB ratio of 2.39 (the league is 2.36).

The next area I will look at it is Stewart’s ground-ball/fly-ball tendency. According to milb.com, Stewart currently sports a 1.73 GO/AO ratio. This suggests that he is an extreme ground ball pitcher, whereas his 1.24 GB/FB ratio (according to Baseball-Reference) pegs him as more of a moderate ground ball pitcher². In any case, Stewart appears to be, at the very least, a moderate ground ball pitcher. The importance of this ground ball tendency is easy to see: opposing hitters have a .079 isolated slugging percentage against Stewart, well below the league average of .119.

What it Means

Just looking at Kohl Stewart’s numbers leads to an interesting conclusion: he appears to be the classic “Twins pitcher”: low K-rate, low BB-rate, high GB-rate. Although it would be nice to see Stewart posting higher strikeout numbers, I would argue that a low walk rate and a high ground ball tendency are more important at this stage in his career: you rarely see a fly-ball pitcher become a ground-ball pitcher and given the numerous reports raving about Stewart’s “stuff,” I remain optimistic that he can increase strikeout totals; I would be more nervous if he was walking lots of hitters. If Stewart can continue to generate ground balls, limit walks, and increase his strikeout, he will be poised to become an ace. But even if he doesn’t become a strikeout machine, his excellent control and ground ball inducing abilities at this young of an age should allow him to be an effective pitcher for years to come.

Last year, the Twins limited Berrios to 103 IP. Stewart has thrown just over 70, so only expect him to log about 30 more before the Twins shut him down. Unless he becomes a dominant strikeout machine before the season ends, the Twins will have an interesting decision about where to start Stewart next spring: do they promote him to Ft. Myers and see how he fares or do you hold him back in Cedar Rapids for a month or two until he displays an improved strikeout ability? I would lean towards the conservative approach—after all, Stewart would still be one of the younger pitchers in the league—but hopefully Stewart will finish strong and make that decision for us.

¹ That being said, a prospect’s age should not enter the conversation when considering whether or not they should be promoted: a player has mastered a level when they have mastered the level, and that has absolutely nothing to do with how old they are. In other words, although we shouldn’t be scared if Stewart is struggling, we shouldn’t promote him just because he’s young.

² Considering that a higher percentage of fly balls are outs than groundballs, it is surprising that Stewart’s GO/AO ratio is significantly higher than his GB/FB ratio. It is possible that this is the result of an extraordinary number of weakly hit groundballs, or it could be a coincidence.