Why Eovaldi would be a perfect fit in Houston

After a pair of Tommy John surgeries, multiple trades and a year out of baseball entirely, Nathan Eovaldi just pitched as well as he ever has in helping the Red Sox win the World Series
But is there potential for him to get even better?
MLB.com's Jon Morosi reported Tuesday that the Astros are showing "continued interest" in signing Eovaldi. The righty could pitch in front of his hometown hero, Nolan Ryan, at Minute Maid Park, instantly join another World Series contender and bolster a rotation already stacked with a pair of aces in Justin Verlander and Gerrit Cole. 

It's the latter benefit that hints at the most exciting possibility of all: Eovaldi seems like the perfect next project for Houston's vaunted coaching and analytical staffs. In two successive seasons, the Astros have taken a pair of brand-name starters in Verlander and Cole (not to mention others, like Charlie Morton and Brad Peacock) and helped them become better pitchers by presenting data and tweaking their mechanics. Here's what Cole -- who went from an ace stuck in neutral in Pittsburgh to a Cy Young Award contender in Houston -- told ESPN's Marly Rivera last June about the Astros' staff:
"They continually put me in a better spot. That's given me the physical ability to go out and apply what I've learned here in such a short time. It's basically throwing the four-seam. Run the four-seam more."
The four-seam fastball is the key connection between Cole and Eovaldi. Like Cole, Eovaldi owns a high-octane four-seamer; at 97.1 mph, per Statcast™, it was the second-fastest on average among 113 starters who threw at least 500 of those pitches last year (Cole clocked in right behind him). But, as MLB.com's Mike Petriello noted several years ago, Eovaldi's four-seamer doesn't carry the type of spin that elicits the number of whiffs one would expect from a pitch that fast. In fact, Eovaldi's heater carried very similar basic parameters to Cole's in Pittsburgh.
Cole and Eovaldi's four-seamer similarities

Cole, 2017 (PIT): 95.9 mph / 2,164 rpm / 19.8% whiff rate*
Eovaldi, 2018 (TB/BOS): 97.1 mph / 2,135 rpm / 24.3% whiff rate
*Whiff rate = Misses / Total swings
For context, Major League pitchers averaged a 2,263 rpm spin rate on four-seam fastballs in 2018, and a whiff rate of 20.5 percent on that pitch type. Four-seamers with spin rates above 2,300 to 2,400 rpm tend to elicit more whiffs and popups. Once he joined the Astros, Cole not only began throwing his four-seam fastball more while putting his two-seamer on the backburner; he also saw his four-seam spin rate jump about as much as any pitcher has seen since Statcast™ launched in 2015. Cole credited the Astros and Verlander in numerous interviews with helping him change both his hand positioning and spin axis on that pitch, while also re-adjusting his mindset toward attacking the top of the strike zone.
"He found out that he had good four-seam hop, and he didn't really know how to use it," Verlander told MLB.com's David Adler of Cole's adjustments last year. "[In Spring Training] we were playing catch, and I was pointing out the ones that were good and the ones that were bad. And they were basically the opposite of what he thought."
Cole added, "To me, it seems like I'm yanking the ball. But to [Verlander], he's like, 'You're actually staying behind the ball and getting better rotation. It's actually doing what you want it to do. It's not fading, it's jumping.' I took that trajectory and moved it to my spots. Trying to chase that type of action, that was a big day for me."
Cole's four-seamer transformed from a somewhat disappointing pitch, given its velocity, to one of baseball's very best in 2018. The righty's 250 swings-and-misses on the four-seamer ranked third behind Verlander and Max Scherzer, and the .185 average he allowed on the pitch was also MLB's third-best mark (min. 200 at-bats). Along with throwing more curves and sliders, Cole's ascendance was due in large part to his four-seam spin jump (a 2,379-rpm average in '18, 12th-best among qualified starters).

So, could Eovaldi see the same kind of improvements under the Astros' tutelage? It's worth noting that Cole's transformation was rare; not everyone can simply add spin to their pitches, because it is mostly an inherent skill as opposed to one acquired. But if any team could help Eovaldi improve his heater, it would be the Astros, who, as The Athletic's Eno Sarris found recently, have helped a handful of pitchers find small spin gains in recent seasons.
And here's the most encouraging sign for the Astros: We've already seen Eovaldi flash his high-spin potential. Statcast™ has tracked a number of Eovaldi four-seamers with spin rates over 2,400 rpm since 2015, including the '18 postseason. Perhaps some simple mechanical tweaks could help him unlock those pitches on a more consistent basis.
Spin isn't the only key to success when attacking big league hitters. Eovaldi, for instance, allowed a .280 average on 2,300-plus rpm four-seamers in 2015-16 before he underwent his second Tommy John surgery. However, he was throwing the majority of those high-spinners down toward hitters' knees and not at the top of the strike zone, where those pitches are most effective. Based on their history with other pitchers, that's a change you can bet the Astros would suggest if Eovaldi signs.
It's Hot Stove season, which means we're making some assumptions here, but with Dallas Keuchel and Morton both currently free agents, it seems likely they will go out and get an elite arm. That said, the Astros haven't signed Eovaldi yet, and his injury history can't be forgotten. A pair of Tommy John surgeries means Eovaldi's career could turn for the worse on any given pitch, and he just worked overtime to help deliver the Red Sox a World Series title. Maybe the Astros would avoid mechanical changes altogether if they felt it would put additional strain on that right elbow. Still, Eovaldi already took so many steps forward as a pitcher last season that it's tantalizing to imagine him getting even better. His cutter became a major weapon, and remember: He was already doing this to the Dodgers' Justin Turner during his heroic World Series Game 3 relief appearance with the fastball he currently owns:

Eovaldi has been linked with his potential ever since the Dodgers gave him a $250,000 signing bonus out of high school 10 years ago. Maybe the Astros' rumored interest signals their belief that they can help him unlock that next level in 2019.