Eddie Rosario Continues to Evolve

Last year, you may recall that I published a quick post on Eddie Rosario's plate discipline dramatically improving, which in turn made him a much better hitter. Rosario finished 2017 with the best walk and strikeout rates of his major league career and, for the first time, an above-average line: .290/.328/.507 with 27 homers, good for a 116 wRC+.

I now call your attention to another significant development in Rosario's career. Through Tuesday's games, only 19 qualified hitters (one of whom, somehow, is teammate Eduardo Escobar) lead Rosario in isolated slugging. Rosario leads the Twins in batting average, hits, home runs, slugging percentage, OPS, and wRC+; he shares the lead in runs with Brian Dozier.

Eddie Rosario is now a slugger.



This is a major step for a player trying to prove he belonged in the majors last Opening Day. And the way he's developed has resulted in a unique profile without a perfect comparison in recent memory.

When he was first called up, Rosario hit the ball in the air a good amount. In his last few years in the minors, and in his first in the majors, he hit about as many grounders as he did flies. Over the previous two seasons, he started hitting the ball on the ground more.

As you probably figured out, however, he has diverged from that path in 2018. Because I like graphs, let's look at one that shows us how much he's diverged.

You can see here that this was a change that's been in the making for some time. Somewhere in mid-2017, his ground ball rate tailed off dramatically and has since continued to decline. Now, Rosario's single-season fly ball rate (44.0 percent) is easily the highest of his MLB career. His single-season average launch angle (19.1 degrees) is also easily the highest of his MLB career.

He's clearly generating more loft, which, combined with a bump in his exit velocities, is resulting in more extra base hits.

But that's not the only change to his batted-ball profile. Between 2016 and 2017, Rosario hit distributed the ball similarly to how the average major-leaguer did. He pulled the ball less than 40 percent of the time, he hit it up the middle about as much as he pulled it, and he went opposite-field about a quarter of the time. Pretty normal.

But in 2018, Rosario is a dead-pull hitter. Regardless of batted ball type, his pull rates have leapt.

Like a classic cleanup hitter, Rosario is hitting the ball hard, he's hitting it in the air, and he's hitting it to his pull side. In fact, at a glance, he kind of looks like Adam Dunn:

Of course, this is not a totally apt comparison. Rosario is hitting .314 this season (again, through Tuesday). Over his whole career (spent mostly in an era of higher batting averages), Dunn hit .237.

Rosario, you see, has become an unusual hitter. He doesn't neatly fit into any archetype. You can find attributes of players that fit, but nobody's profile is quite the same.

We've already discussed what happens when he hits the ball. Let's return to the subject of last year's post: his approach.

FanGraphs has PITCHf/x or Pitch Info plate discipline data going back to 2007. Since then, 4555 batters have made 150 plate appearances or more in a single season. These are all 4555, plotted by the differences in their Z-Swing and O-Swing rates and Z-Contact and O-Contact rates. Rosario's 2018 season is represented by the big yellow point.

The further to the right a player is, the larger the difference is between their swing rates in or out of the strike zone. Usually, a higher difference is a good thing: The batter is swinging at more strikes and fewer balls.

The higher a player is, the larger the difference is between their contact rates in or out of the zone. Often, a higher difference is a bad thing: The batter is missing more often when he swings at balls. Strikeout-prone players like Austin Kearns and Aaron Altherr are near the top. However, this might not indicate a proclivity to strike out if the batter doesn't swing at many balls in the first place. Take 2012 Yonder Alonso, whose Z-Contact % - O-Contact % ranks in the top 10 percent, but who struck out at a lesser rate than the league average because he laid off bad pitches.

In my spreadsheet, I made a ratio out of these two statistics. Those with the largest ratios are usually one of two types of hitters: those with both good plate discipline and contact skills, like Joey Votto and Jason Kendall; and those who don't walk often but still make as much contact on pitches in the zone as they do on pitches out of the zone, like Wilmer Flores and Kevin Frandsen.

2018 Rosario, whose ratio ranks in the 97th percentile, fits into the latter group of hitters.

As I previously covered, Rosario made massive improvements to his approach last year. If you read the original post, this graph will look familiar. It's his rolling swing rates on pitches in and out of the strike zone since his debut, updated to this season.

He certainly still likes to swing, and his O-Swing rate spiked a little at the beginning of the season, but it's since stabilized. As a result, his walk rate remains passable. His ability to make contact on pitches out of the zone also helps keep his strikeout rate at a career low.

But unlike Flores and Fransden, Rosario is far from an offensive lightweight. Remember: His batted-ball comp was Dunn. He's a legitimate power threat – but he's no sluggish brute or typical three-true-outcomes hitter. He has a unique combination of tools and tendencies that make him a legitimate force in the heart of the order.

There are more well-rounded hitters, but the Twins are fortunate to have one this capable.

Statistics, unless otherwise noted, via FanGraphs.