Miami Marlins pitcher Nathan Eovaldi's fastball, then and now

The Miami Marlins got a solid, unspectacular performance from Nathan Eovaldi last night against the Los Angeles Dodgers, but he was especially impressive in throwing one pitch: the fastball. Eovaldi's fastball hit triple digits three times last night, including twice in a row to end an inning with a strikeout and get out of a jam. The pitch averaged 97.9 mph last night, and those numbers are not short of fantastic for a pitcher who has shown significant change since last season.

This change has been so spectacular that scouts are starting to take notice. This Baseball Prospectus article (subscription required but recommended) discusses one scout's view on the offering after he dominated the Atlanta Braves a few weeks ago.

Marlins RHP Nathan Eovaldi: "He might have the best fastball I have seen all year. The off-speed stuff is still a work in progress, but the slider is definitely useable. There's no doubt in my mind he would be an elite closer, but he may become a middle-of-the-rotation starting pitcher, and he was better than that on Saturday against the team with the best record in baseball."

The fastball has been extremely impressive; according to raw Pitch F/X data provided by FanGraphs, no pitcher with at least 70 innings to his name has a faster pitch than Eovaldi's fastball. According to the adjusted data provided by Brooks Baseball, Eovaldi's fastball is clocking in at a cool 97 mph on average. Everything points towards a drastic improvement in Eovaldi's work.

Except, strangely enough, the actual results.

Surprisingly, Nathan Eovaldi's much-improved fastball. which we have profiled before, has not produced the results one would expect when compared to his old fastball that sat 2.5 mph lower in the velocity column.

*Includes Eovaldi's so-called two-seam fastballs.

The early results have not borne fruit for Eovaldi this season. Despite the uptick of almost 2.5 mph, we see almost no change in the results of fastballs that were not put into play. Hitters are missing the exact same amount of pitches and are getting balls and called strikes at almost identical rates. This is happening despite fewer swings at the fastball. The same goes for foul balls, which remain exactly the same from last season.

But we know that we have seen a difference in Eovaldi's work, hence the decreased ERA and FIP. If it is not from the fastball's results on balls not in play, how about the balls that did end up in play?

This seems to be where the difference resides. The Marlins are only seeing changes in fastballs that are put into play. Eovaldi is getting fewer of those than before, but the results of those pitches thus far have been underwhelming for hitters.

To a degree, it is understandable that a faster fastball would give you better results on balls in play, but we need to be careful how we interpret that data going forward. Eovaldi is unlikely to continue to suppress hitters like with the fastball, and eventually his success needs to come from not just weaker contact but better strikeout and walk numbers. So far, his fastball appears to be under control compared to his mediocre breaking pitches, but despite its high velocity, it is not fooling anyone. All of this improvement will be for naught if he cannot convert velocity into strikeouts.

But this is why I rated Eovaldi as the pitcher with the most promise among the three questionable young starters. That fastball velocity caps his floor as back-end reliever / closer potential, but the ceiling remains significantly higher than both Jacob Turner's and Henderson Alvarez. If he can figure anything else out, a 97 mph fastball will carry him a long way in Miami.