Why are Yankees pitchers struggling with their two-seam fastballs?

When CC Sabathia went through his highly publicized Captain Crunch-induced drop in velocity, he was like a deer in headlights when he threw his fastball. In 2013, he surrendered 14 home runs when throwing his fastball. Like many other pitchers, his lack of success with a traditional heater drove him to make the transition from a four-seam fastball to a two-seam fastball with the hope of keeping hitters out of the seats.

Guys like Greg Maddux, Roy Halladay, and Brandon Webb glamorized the groundball pitcher for a lot of fans, possibly because they it was a great underdog story. In an era dominated by heaters that can light up a radar gun, pitchers who live in the high 80's/low 90's and still put up Cy Young-caliber numbers will always be admired. So for pitchers like CC and Ivan Nova, whose four-seam fastballs get hit to the moon on a regular basis, throwing a two-seam fastball seems like the perfect solution.

Unfortunately, both CC's and Nova's two-seamers have been hit very well this year. In an even more disheartening development, both pitchers are still surrendering home runs at a rate above league-average. The plan was for both of them to pitch to more groundballs, keep hitters in the stadium, and be effective middle of the rotation starters, but somewhere along the line, something went wrong.

A study by The Hardball Times seems to suggest that their mechanics are the culprit. According to the study, lower arm slots lead to greater platoon splits. Nova throws from a ¾ arm slot, while CC's arm angle is a bit higher. However, Sabathia's release point has dropped in recent years, possibly exacerbating his struggles against right-handed hitters. Here are the splits from Nova and Sabathia on their sinkers this season, courtesy of Brooks Baseball:

Another possible reason for these drastic splits is command. It is well known that Sabathia, with his decreased velocity, needs to locate his pitches extremely well to avoid any major damage. But lost in Nova's recent struggles are the extremely encouraging numbers he put up in 2013. That year, he had a 3.10 ERA and held lefties to a respectable .302 batting average and a .333 SLG% against his two-seam fastball. While an ISO of .031 is tough to sustain for anyone, Nova flashed the ability to do some sort of damage control against lefties. Here is how he located his sinker against lefties in 2013, vs. in 2015:

In his 2013 heatmap, the red dot is right on the outside edge, but this year it has moved back over the plate. Command issues are to be expected after returning from Tommy John Surgery, so there is still a chance that Nova could return to form next year and dot the outside edge against lefties once again.

Unfortunately, as the study from The Hardball Times points out, throwing sinkers from a lower arm slot is bad news when facing hitters in the opposite batters box. It is something for the Yankees to consider. For pitchers like Nova and Sabathia, the best bet is to mix in a good four-seam fastball and/or a cutter, as Brandon McCarthy did last season for the Yankees. Hopefully, Larry Rothschild can work his magic in the offseason, and 2016 can be the year these two pitchers finally put something special together.

*Data is courtesy of Fangraphs, Brooks Baseball, and Baseball Savant