Eddie Rosario Is A Lot Like Nolan Arenado Now

When you drafted Eddie Rosario a couple of months ago, you probably took him after the first 75 players were already picked. He may have even been the third outfielder you selected. Yet based on what Rosario has done over the nearly two months since opening day, you might rightfully believe you snuck a player with first-round value onto your roster, long after the elite hitters came off the board.

Rosario has played in all but two of the Twins’ 47 games to date, and his total of 13 home runs has him on a pace to finish in the 40-to-45 range. He is also on a trajectory to finish with more than 120 runs and 120 RBIs. Even putting those numbers into the context of this season’s power explosion, it’s clear that Rosario is having a dramatic breakout campaign, as those marks would obliterate his previous career highs (27 home runs, 87 runs, 78 RBIs).

What is truly remarkable is that Rosario is accomplishing this without become a more selective hitter. His plate discipline is notoriously poor, and his O-Swing% of 42.2 percent is the seventh-highest among qualified hitters and 0.4 percentage points above his career mark. Instead of laying off out-of-zone pitches, Rosario simply got better at making contact on those pitches and hitting them with more authority. He increased his Contact% on pitches both in the zone and out of the zone, with the latter mark rising from last season’s 69.8 percent to a career-high 74.7 percent. Rosario also bumped up his average exit velocity on batted balls hit from outside of the strike zone, raising it from 84.1 to 87.4 mph, year over year.

The breakout we are currently witnessing from Rosario bears a sneaky resemblance to Nolan Arenado’s big breakthrough in 2015. That year, he made the jump from 18 to 42 homers (albeit in 198 more plate appearances) and more than doubled his RBI output from 61 to 130. Arenado made those strides, even though his O-Swing% ticked slightly upward, from 38.1 to 38.5 percent.

And you know who else resembles the 2015 version of Arenado? The 2019 version of Arenado. In 2016, he broke out to an even higher level, maintaining his power gains from the year before while swinging at fewer out-0f-zone pitches and boosting his walk rate and OBP. Arenado continued to be a more selective hitter right through to last season, but so far in 2019, he is swinging at out-of-zone pitches at a 40.9 percent rate — his highest O-Swing% since his 2013 rookie season.

If we stack their season-to-date stats side-by-side, we see there is very little difference in Rosario’s and Arenado’s plate discipline indicators. Neither is getting many pitches in the zone, and both are chasing out-of-zone pitches frequently. That approach is working for both hitters as they are well above the major league average for O-Contact% (61.8 percent). They are also well above the .307 median for xwOBA on out-of-zone pitches (min. 500 total pitches).

That latter achievement is especially notable, as there is a strong relationship between how often hitters avoid swinging at out-of-zone pitches and how well they are expected to produce when they connect with an out-of-zone pitch. In other words, it appears that choosy hitters are good at choosing the best pitches outside of the zone to hit. That relationship is clearly depicted in the graph below, but it also shows that Rosario and Arenado have decent xwOBAs on out-of-zone pitches while being anything but selective.

That lone dot in the upper-left portion of the graph…that’s Mike Trout. That’s Kevin Pillar in the lower-right corner. The majors’ most and least selective hitters are also the best and worst hitters, respectively, on out-of-zone pitches, and the hitters in between fall in line with the general trend for the most part. Yet Rosario and Arenado have xwOBAs on out-of-zone pitches that are typically 50-to-80 points higher than other hitters who chase out-of-zone pitches at an extremely high rate.

This is a new development for Rosario, who posted O-xwOBAs of .261 and .303 in each of the last two seasons. This season’s higher mark reflects the increased exit velocity with which he is hitting out-of-zone pitches both in the air and on the ground.

So why is it, then, that Rosario’s actual wOBA in 2019 is just .335 — 25 points below his xwOBA and five points lower than his wOBA from last season? Blame the BABIP gods. Rosario has lost 79 points on his BABIP since last season (from .316 to .237), which is the fifth-largest drop among hitters with at least 150 plate appearances. Yet Rosario’s 2019 batted ball profile is nearly identical to last season’s, with the lone exception of a decrease in line drive rate from 20.3 to 16.6 percent. Not only is it reasonable to expect Rosario to increase that rate closer to his previous norm, but it only explains part of his BABIP decrease. With career-low swinging strike and strikeout rates and an increase in average exit velocity, Rosario should be hitting well above his current overall .260 batting average. Baseball Savant’s xBA has Rosario at .276, and if he increases his line drive rate, his rest-of-season batting average could be even higher than that.

Though his surface stats don’t suggest it, Rosario just might be elevating himself to elite status. The key question is over how much we can trust his season-to-date stats, now that we have reached the latter portion of May. His big gains have been in SwStr% and average exit velocity, and we are at the point where the samples of data are large enough for those measures to stabilize. The upper bound of the 95 percent confidence interval on Rosario’s 10.4 percent SwStr% is 12.4 percent, which is 0.3 percentage points below his rate from 2018. So there is some chance he could approach last season’s mark, but it’s highly likely he has made real improvement. His overall average exit velocity is 90.1 mph with a lower bound of 88.1 mph. That’s nearly one full mph higher than last season’s average of 87.3 mph.

We are deep enough into this season that we can be pretty sure that Rosario has made legitimate improvements in his frequency and quality of contact, both on pitches outside of the strike zone and on all pitches overall. While we can rule out random variation as an explanation for his improved indicators up to this point, we can’t be as certain that something in his approach won’t change in midseason that would cause him to regress.

For those willing to take that chance, there is an opportunity to trade for Rosario at what could turn out to be a bargain price. His upside is that of an outfield version of Nolan Arenado, circa 2015, complete with 40-plus homers and 120-plus RBIs.