The difference between Jose Fernandez and Nathan Eovaldi in the strike zone

What makes it possible for Fernandez to fool hitters in the strike zone? - Brett Davis-USA TODAY Sports

Miami Marlins hurlers Jose Fernandez and Nathan Eovaldi are both working in the strike zone to a large extent and finding success. But what differentiates the overwhelming success of Fernandez and the still-questionable future of Eovaldi?

The Miami Marlins have two young fireballing right-handers who are off to fantastic starts in 2014. Jose Fernandez has picked up right where he left off last year, whiffing an astonishing 37 percent of batters faced and posing a sub-2.00 ERA and FIP to match. Meanwhile, Nathan Eovaldi is "only" striking out 23 percent of his batters faced while nary walking a batter and putting up an ERA and FIP in the 2.00's. Both guys are doing it in part by throwing hefty fastballs; according to raw Pitch F/X data, Eovaldi has the fourth-fastest fastball among starters this year at 95.4 mph, while Fernandez is fifth at 95.0 mph.

One of the interesting things that have distinguished the two is that both starters are working often in the strike zone. Over the course of their Marlins careers, both Eovaldi and Fernandez have pitched about 200 innings for the team. In those 200-plus innings, Fernandez has thrown 54.8 percent of pitches in the strike zone, and Eovaldi is following close at 54.0 percent. Both pitchers have found success attacking hitters in the strike zone. But their levels of success have varied, and there is a key and obvious difference when you look at the plate discipline numbers for them.

The key that separates them is how hitters respond to those pitches in and out of the strike zone. Fernandez has relied a little less on his fastball than Eovaldi, throwing it in 56 percent of his pitches versus Eovaldi's 61 percent mark over their time in Florida. But the key is that Fernandez has other pitches that can not only work in the strike zone, but fool hitters to a large degree. His curveball, in particular, is a devastating pitch that gets both whiffs and called strikes with great frequency. Since 2013, Fernandez's curve has registered a 1.2-to-one balls to called strike ratio. When hitters do swing, they whiff on 36 percent of their swings, and they hack at a 48 percent rate. Those numbers all dwarf Eovaldi's marks with his primary breaking pitch, the slider. Eovaldi has not been able to put it in the strike zone consistently (2.9-to-one balls to called strikes) and its whiff rate is below the league average.

The difference in breaking pitches leads to a fundamental difference in mentality for hitters facing Fernandez and Eovaldi. In Fernandez's case, the fastball-curve combination is so potent that hitters rarely know what to look for on any given count, especially since Fernandez can throw either pitch for a strike. The curveball has a natural edge in called strikes that sliders usually do not have, but the slider does have the advantage of better whiff rates. Since Fernandez's curveball is above average, it lead to even more problems for hitters. You can see that they are discombobulated at the plate by their rate of swings in and out of the zone. Despite near-identical zone percentages and swing rates, Fernandez has induced a swing on just 57 percent of pitches in the strike zone and 32 percent of pitches out of the zone.

Compare that to Eovaldi's numbers. Because Eovaldi's slider has non-tricky movement and hitters have gotten decent reads on the pitch, batters know what to swing at and what to lay off of. In his time with the Marlins, Eovaldi has induced a 26 percent rate of swings out of the zone and a 64 percent rate of swings in the zone. Among Marlins starters since 2009 with at least 100 innings thrown, that is the second-highest rate of swings in the zone and the lowest rate out of the zone. It flies completely contrary to Fernandez, who ranks second only to Ricky Nolasco in swings out of the zone and lowest in swings in the zone. Generally speaking, you want hitters to chase out of the strike zone and lay off of pitches in the zone for called strikes. That is exactly what Fernandez is doing, and that is why he has been so successful. Alternately, hitters have caught on to Eovaldi.

How can Eovaldi solve this problem? It would help to develop better breaking pitches, but that may not be fully possible for him. Then again, at this point, does he need to fix this? Eovaldi's fastball is still elite enough to avoid getting hit hard by opposing hitters, even though they know he has lived in the strike zone. It is possible that he carves out a career like this and never becomes Jose Fernandez. And that is perfectly fine, because Jose Fernandez is a once-in-a-lifetime talent who does magical things with baseballs. Eovaldi does not need to match his prowess to be good; he simply needs to continue doing what he has done so far in 2012 to be a worthy right-hand man to Fernandez in the rotation.

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