Fact #1: Sonny Gray is a good pitcher. Since his debut in 2013, he's accrued 12.0 fWAR in 770.1 innings pitched, and his career ERA and FIP are both around one standard deviation above league average. Add in the fact that he's still in his arbitration years, and the Yankees were very, very fortunate to get him for the price that they did.
Fact #2: Sonny Gray has developed a dinger problem. As PSA's own Tyler Norton has noted, Gray, previously known for generating ground balls and limiting home runs, has found that difficult since coming over to Yankee Stadium. In 11 starts and 65.1 innings with the Yankees, Gray has recorded a FIP of 4.87 and a HR/9 of 1.52, both well above his career averages. It's still a small sample size, but given the much more friendly confines of Yankee Stadium III compared to the Oakland Coliseum, Gray's dinger-itis probably can't be chalked up to mere bad luck.
Has Gray tried to adapt to his new home ballpark by changing his pitching style? If he has, it isn't showing in the data. Tyler notes that Gray's heatmaps and release points haven't really changed from his Oakland days. In addition, Gray's pitch mix has generally remained the same over the course of his transition to the Bronx. According to Pitch Info's pitch type classifications, he's reduced his curveball usage while upping his slider usage, but his fastball/breaking ball ratio hasn't really changed. Gray's bread and butter is still his four-seam and his sinker, and the two pitches amassed nearly two-thirds of his total pitches in 2017.
It's hard to fault a guy for sticking to his guns, but this author believes that Gray could benefit from a change in his pitch usage. While his sinker used to kill gophers in past years, it hasn't found the same success in the Bronx, as it allowed an ISO of .187 and a HR/FB rate of 30.6% in 2017. Likewise for his fourseam, which generated a HR/FB rate of 13.6%. What were once Gray's most reliable weapons have become his most homer-prone pitches, which is never a good sign for a pitcher.
Fortunately for Gray, he has other quality offerings to make up for his diminishing fastballs. His slider is his piece de resistance, having been worth 7.9 runs in 2017 and 5.6 runs with the Yankees. Batters managed just a .141/.168/.212 slash line against it in 2017. It's a terrific pitch that misses bats about a fifth of the time, and Gray should probably be using it much more than the 19.6% he recorded in his time with the Yanks. Gray also has a solid curveball which generated a swinging-strike rate of 12.9% in 2017, yet he only threw it 13.0% of the time in the Bronx. All of this seems like inefficient usage of good pitches. The solution seems simple: why not throw less fastballs and throw more sliders/curveballs?
Leading with breaking balls has become the pitching fad of progressive MLB teams in recent years, and the Yankees are no strangers to this strategy, with followers such as Masahiro Tanaka, CC Sabathia, and Jordan Montgomery. In an age where everyone hits 20 homers, and in a park where cheapies happen on the daily, the most obvious way to limit homers is to limit contact and generate whiffs. Gray's magnificent slider and quality curveball should help him to do just that. All he has to do is throw them a bit more.