Breakout Breakdown: Nathan Eovaldi

By the end of this weekend, we may have seen our last innings of baseball for this season, but we will almost certainly get at least one more chance to watch Nathan Eovaldi. (I am personally just rooting for more baseball.) He has grabbed the spotlight this postseason, excelling in a pair of starts and in three relief appearances in which he set up for Craig Kimbrel. If needed, Eovaldi could be used as the bridge to Kimbrel again in Game 3, but if not, then we may see him as the Red Sox’s Game 4 starter.

It’s not only for the potential of postseason heroics that it’s worth taking one last peek at Eovaldi in 2018. It’s been a breakout season for the 28-year-old, though his 6-7 record and 3.81 ERA would suggest otherwise. In his first season back from his second Tommy John surgery, Eovaldi was better than ever in just about every regard aside from ground ball and home run rates and ERA, and the latter was inflated by a 67.3 percent strand rate. His walk (4.4 percent), swinging strike (10.7 percent) and O-Swing (33.9 percent) rates were all career bests, and his 22.2 percent strikeout rate was nearly four percentage points better than his previous high water mark (18.5 percent in 2016).

Though Eovaldi was not particularly close to his career-low ERA of 3.39 set in 2013 with the Marlins, his 1.13 WHIP is his first-ever mark below 1.30.

One thing that didn’t change for Eovaldi this season, fortunately, was his fastball velocity. He made his season debut (and Rays debut) on May 30, and right away he was averaging just shy of 97 mph on his fastball. However, his arsenal had a different look, as he was throwing a cutter roughly 20 percent of the time through his first four starts. By the time the Rays traded Eovaldi to the Red Sox in late July, he was regularly using his cutter for more than one out of every three pitches. (Back in August, David Laurila recounted the story behind Eovaldi’s re-introduction of the cutter back into his arsenal.)

The cutter was a reasonably effective pitch for Eovaldi during the regular season (0.94 wCT/C, .314 wOBA allowed), but it was not directly related to his spike in strikeout and swinging strike rates. Just 9.0 percent of Eovaldi’s 577 cutters resulted in a swinging strike and the pitch generated a 13.6 percent strikeout rate.

The strikeout rate on Eovaldi’s fastball soared from 12.2 percent in 2016 to 29.7 percent in 2018, while the walk rate on his fastball swooned from 14.5 percent to 4.3 percent. He was able to improve his strikeout and walk rates, as well as increase his swinging strike rate on his fastball from 7.2 to 10.7 percent, even though he located the pitch much higher this season, venturing much more frequently above the top edge of the strike zone.

Eovaldi made this work by getting more chases on out-of-zone pitches. His fastball O-Swing% increased from 23.8 percent in 2016 to a career-high 29.4 percent this year. As the heatmap below shows, Eovaldi avoided contact on fastballs above the zone at a much lower rate than he did in the center and lower portions of the zone. Even when Eovaldi was locating his fastball in the upper third of the strike zone, he was inducing less frequent contact than in the center and lower portions.

While Eovaldi had greater success with his fastball by locating it higher, he also improved his results with his slider by throwing it farther down and away from right-handed hitters (against whom he had a 21 percent usage rate, per Brooks Baseball). He still kept his slider in the strike zone frequently, compiling a 50.0 percent Zone%, but it was a much harder pitch to put in play than in the past. Hitters amassed a 78.5 percent Z-Contact% on Eovaldi’s slider, which was nearly five percentage points lower than his previous career best.

Mixing up his arsenal and pitch locations allowed Eovaldi to experience a new level of success, especially in terms of his skill indicators, but the improvement in strikeout rate was heavily backloaded. Through the end of August, Eovaldi had a 19.7 percent K%, which would still have been a career high, though by only 1.2 percentage points. Beginning with his first start in September, he changed his horizontal release point (see below). Then through his 20 innings that month, Eovaldi struck out 27 batters for a 33.8 percent K%.

That late-season surge in strikeouts amplified the magnitude of Eovaldi’s breakout, but going into 2019, fantasy owners should bear in mind that he finished with just 111 innings. If he had extended his season in order to get something closer to a full year’s worth of innings, would he have regressed to his pre-Tommy John levels or built on his progress? Eovaldi’s postseason success lends some credence to the latter scenario (though he is sporting a more muted 17.5 percent K%), but we will never know. It is clearly risky to assume that Eovaldi would have been just as good over 165 innings as he was over the 111 innings he actually did pitch in the regular season.

Given that Eovaldi’s strikeout rate was not far out of line with his previous marks for the first three months of his season, it won’t make sense to count on him to sustain his K-rate breakout next year. It may not be any more sensible to expect him to sustain the improvement in his walk rate, which was 0.6 percentage points better than his previous career-low and 2.7 percentage points lower than his career average. As I will explain in an upcoming column, there are few starting pitchers who are able to sustain notable improvements in their walk rate beyond a single season. Eovaldi has already managed to do that once in his career, as he has never come close to approaching the 8.9 percent walk rates he posted in 2012 and 2013, but a second sustained dropoff in walk rate would truly defy the odds.

Should Eovaldi maintain his skill gains from this season, he could finish as a top 40 pitcher in 2019, regardless of where he signs this offseason. That would assume he stays healthy and doesn’t regress. Those don’t seem like safe bets, so it’s best to pursue him only after the first 250 players are off the board.