Entering the 2015 season, Nathan Eovaldi's goal was simple: develop an off-speed pitch. His brief foray into throwing a circle change in Miami was a disaster, so he worked with Larry Rothschild to develop a splitter instead. For the first part of the season, that pitch looked more like a forkball, staying around the mid 80's with very little spin. Then, as his velocity charts show, he tweaked that pitch into a true splitter, with a spike in velo in June:

Since June 26, Eovaldi was a force in the Yankees rotation, with an ERA of 3.46 and an FIP of 2.90. He also struck out 7.7 batters per nine innings. While that figure is not the most impressive out there, a major plotline of his career arc was his inability to strike out hitters despite his 100 mph fastball. Progress in that regard was definitely welcomed with open arms.

Perhaps the most exciting part of Eovaldi's improved splitter was that for the first time, Nasty Nate showed traces of deceptiveness while pitching. Before that fateful day on June 26, lefty hitters had a Whiff/Swing ratio of 13% against his fastball, according to Brooks Baseball. After integrating a splitter, which was used primarily against lefties, that figure jumped above 20%. Righties had a yearlong Whiff/Swing Ratio of 13% against the heater.

Lefties have always teed off against Eovaldi. If someone were to argue that Eovaldi throws his fastball too often and is too predictable, it would make sense. If someone then argued that Eovaldi's high ¾ arm slot makes it easier for lefties to pick his pitches up, he or she would have a point. Suggesting that he might one day consider adding a cut-fastball to bury on the inside corner against lefties would also make sense. But there is absolutely no reason why righties should have a Whiff/Swing ratio of just 13% against a 100 mph fastball.

Enter: Eovaldi's slider. Here is a gif of Eovaldi's slider in action against the Boston Red Sox.

Evidently, Hanley Ramirez is anything but fooled by the breaking ball. He sits back and doesn't try to do too much, shooting a ground ball up the middle for an RBI single. Eovaldi also hangs this pitch up a bit. But perhaps even more important than the velo and location is the movement. Eovaldi's slider almost appears to feature the big, sweeping tilt that one might expect from a 12-6 curveball, just without the drastic movement. The most effective sliders will look like fastballs for as long as possible, something that cannot be said of the slider shown above.

If Eovaldi wants to finally put all of the pieces together, he will have to refine his breaking ball. He could do what Ivan Nova did and completely abandon his slider, especially since his curve has shown promise. He only threw his curve 9% of the time in 2015, but according to Brooks Baseball, over 50% of his curves were thrown on the first pitch of the at bat. In other words, Eovaldi is confident enough in his ability to command his curveball that he will occasionally try to steal a first pitch strike with it.

If not, he might try to tighten up the rotation on his slider to make it a more effective put away pitch for righties. But it is extremely important that Eovaldi learns to deceive hitters on both sides of the plate. He could throw 110 mph or completely randomize his pitch sequence, but the strikeouts won't come if he cannot get more late movement on his pitches. If Nasty Nate can get just a bit more deceptive with his pitches, he might finally put everything together and live up to his nickname.

*Data is courtesy of Fangraphs and Brooks Baseball.