Shame on me for not recalling this yesterday when I wrote the initial post, but commenters JJToucan and chrisN pointed out to me that Nathan Eovaldi did state that he had started working on a changeup/split-finger fastball hybrid during his final few starts of the 2014 season. That quote actually came from the Bryan Hoch story that I linked to on January 23rd, so double shame on me for missing it multiple times. That's really nothing more than my own forgetfulness. Yes, Nathan Eovaldi has started working on throwing a changeup a new way, and yes, that new way explains the increase in changeup velocity. Via Brooks Baseball, Eovaldi threw 19 of these split-changeups last September and the SSS results were much more encouraging than his earlier changeup numbers. The 90 MPH average is impressive. We don't usually think "changeup" when we think 90+ velocity, but when you're talking about a guy sitting 96 and touching 97, 98, 99 with his 4-seamer and you add some downward movement to the pitch, you can understand how that could be a handful for left-handed hitters.
The swing and contact rates on those 19 pitches speak to that. While only 5 of the 19 pitches were thrown for strikes (26.32%), 7 of them drew swings from the batter (36.84%) and 4 of those swings were whiffs (21.05%). Only 2 balls were put in play out of the 19 split-changes that were thrown, and both of them were hit on the ground. From a slower, straighter, flatter changeup that generated whiffs about 5% of the time and had a .660 SLG against it to a harder pitch with more downward movement that lefties didn't do anything with in the handful of opportunities they had. Sample size aside, that's a pretty drastic turnaround.
To really drive the point home of how differently this split-change acted, peep the pitch location breakdown:
That's 17 of 19 pitches dropping down and out of the zone. That's where you want your swing-and-miss changeups to be located and that's how you get primo results from a pitch you're throwing for strikes less than 30% of the time. The variance in location in terms of inside-outside indicates the lack of command that Eovaldi had for the pitch at the time, but it shows that he was making meaningful, effective changes to his approach and execution of the pitch and that's incredibly promising.
That's what Larry Rothschild has to work with this spring and that's what his big challenge will be. Eovaldi already has the basics down for how to throw this hybrid changeup and where to throw it to be effective. If Rothschild can help him refine his command of it, get him throwing it more to the down-and-away areas of that zone plot to left-handed hitters as an out pitch, and maybe even get Eovaldi comfortable enough where he can start mixing the pitch into his regular repertoire, we could see that big breakout that people have been talking about. Mastering this split-finger changeup is the key to Eovaldi reaching his potential.