Toolshed: Downs' power on the ups

This 21-year-old Dodgers infielder experienced a power surge in 2019, one that pushed him up the Los Angeles prospect list as well as the Top-100 prospect rankings. He heads into the offseason as one of the most buzzworthy youngsters in the game.
No, this isn't another Gavin Lux article. This one is about Jeter Downs. The No. 5 prospect in the Dodgers system -- and MLB.com's No. 87 overall prospect -- showed surprising power in a breakout 2019 campaign and stands out as one of the bigger slugging overperformers among Top-100 prospects.

Continuing its dive into advanced statistics, Toolshed looks at ISO (isolated slugging percentage) this week, particularly how it compares with the expectations given to a slugger by his power scouting grade.
ISO isn't particularly complex -- it's simply slugging percentage subtracted from batting average. The concept is that slugging percentage alone can't tell us everything about a player's power. A player could bat .400, collect all singles and still slug a fairly respectable .400. But none of that would speak to his absent pop. Instead, his .000 ISO tells the tale. ISO isn't a perfect measure of power -- this version doesn't control for speedy runners who can turn singles into doubles or doubles into triples -- but over a long sample like a full season, it can paint an accurate picture.
No. 3 overall prospect Luis Robert led all Top-100 prospects with a .296 ISO, which will not surprise anyone who followed Minor League Baseball in 2019. The White Sox outfielder hit 32 homers and slugged .624 between Class A Advanced Winston-Salem, Double-A Birmingham and Triple-A Charlotte. At the lowest of those affiliates, he had 16 extra-base hits in 19 games, and at the highest, he had 31 in 47. Known for his impressive bat speed from the right side, Robert showed the power that should earn him a spot alongside Eloy Jiménez long-term on the South Side. We knew that.
That's where Toolshed takes things to another level. The folks at MLB Pipeline assign power tool grades to each ranked prospect, and while meant to reflect on the future, they can be used to set baseline expectations for these players' slugging abilities now. To compare prospect ISOs with these tool grades, Toolshed takes the average and standard deviation of each. For the purposes of this column, Triple-A stats were ruled out. As has been very well documented, the Minors' top level adopted Major League baseballs in 2019 and saw historic power numbers as a result. (Overall Pacific Coast League ISO went up from .153 in 2018 to .200 while the International League saw a rise from .137 to .179.) To include Triple-A slugging numbers in a Minor League average would throw off the nature of the experiment. So we didn't.
The average (non-Triple-A) ISO of Top-100 prospects in 2019 was .170 with a standard deviation of 0.055. The average power tool grade for Top-100 prospects is 51.9 with a standard deviation of 6.86. Since these are some of the game's best young talents, it shouldn't be a surprise that average power for them is still slightly above the 50 designation typically given to power.
Using all of this, we can figure out what the expected ISO (or xISO) for a prospect would be based on their power tool and contrast that to the actual ISO they posted in 2019. These were the biggest overperformers among Top-100 Prospects this past season:

Biggest ISO overperformers among top-100 Prospects (Min. 200 AB)

Gimenez was covered in the 2018 edition of this column when he posted a .128 ISO, and his 2019 results went up slightly. That's in part because he set a career record with nine homers, all at Double-A Binghamton, so the level of power is still surprising. But a big reason for his appearance at the top of this table is that expectations are so low compared to those of his peers. The day may come when Gimenez is truly a well-below-average power hitter at 6 feet, 161 pounds. But for now, he's closer to a 45-grade slugger than 35-grade.
That leaves Downs as perhaps the most surprising player here.
The Dodgers shortstop, who turned 21 in July, was the 32nd overall pick in the 2017 Draft by the Reds. He was a solid hitter in his first full season, producing a .257/.351/.402 line with 13 homers in 120 games at Class A Dayton, but didn't quite show enough bat to sneak onto any Top-100 lists heading into 2019. Los Angeles saw something in him, however, acquiring him from Cincinnati along with fellow prospect Josiah Gray and Homey Bailey's contract for Yasiel Puig and three others. 
In the season since, Downs was more than just solid -- he was a legitimate slugger. The right-handed hitter produced a .269/.354/.507 line with 19 homers in 107 games at Class A Advanced Rancho Cucamonga and was even better after an Aug. 20 promotion to Double-A Tulsa, where he went deep five times in 12 games and finished with a .333/.429/.688 line in the regular season. Downs' 24 homers nearly doubled his 2018 output in the category, and his 68 total extra-base hits not only led all Dodgers farmhands -- yes, even more than Lux -- but also placed 10th among all Minor Leaguers. Only Robert (74) and Pirates first baseman Mason Martin (71) had more among players who did not play exclusively at Triple-A. Using Toolshed's methods here, Downs hit more like a 60-grade slugger than an average 50-grade one.
And that's not even counting a postseason run that saw Downs go deep four times and produce a .349/.391/.674 line over 10 games in the Texas League playoffs.

So what changed?
Yes, he got to play in the California League. The Cal League has long been known as a hitter's haven, and while so much of the offensive focus was on the IL and PCL, there was still plenty of hitting to be done in the Golden State in 2019. Cal League batters produced a collective .140 ISO in 2019. Compare that to the .122 Midwest League batters posted during Downs' year there in 2018, and the difference is not insignificant.
But the explanation isn't as simple as a change in venue. Look at Downs' spray charts for extra-base hits in 2018 and 2019.

The right-handed slugger was very pull-heavy in his first full season, at least when it came to extra-base hits, and especially so when it came to homers. All of Downs' long balls went the left-field fence in 2018, according to this spray chart. That was no longer the case in 2019, with six of the 24 going to either center or right. That opposite-field power was also demonstrated in his doubles, with 13 of the 35 going up the middle or the other way, and triples, with all four going in the center-field gaps.

Physical maturation could explain part of the difference, but the type of contact the middle infielder made in the LA system differed from that he made with Cincy. Downs remains primarily a flyball hitter, putting the ball in the air 53.4 percent of the time in 2019 -- the 11th-highest flyball rate among the 900 Minor League batters with at least 400 plate appearances. But he also got the ball off the ground more often with his groundball rate dropping from 31.7 percent to 24. That was mirrored by a rise in line drives (17.9 percent to 22.6) over the same span. More balls off the ground meant more balls out of the infield and better chances at extra bases, regardless of venue or league.
Does this mean it's time to start thinking about Downs as a plus power hitter, alongside prospects like Robert, Jo Adell and Sam Huff? Not yet. As Gimenez showed, just beating expectations doesn't mean those expectations will change over the long term. At 5-foot-11, 181 pounds, Downs won't be confused for a stereotypical slugger anytime soon. But he is worthy of notice, and he's about to get plenty after climbing into the Top-100 for the first time. It'll be interesting to see how the power plays against upper-level arms, but if he can keep showing more all-fields pop, he could be the Dodgers' Next Big Thing in 2020.
Below are the rest of the top ISO performers among Top-100 prospects from the 2019 season, as well as the biggest underperformers, according to ISO, xISO and power-tool grades. (Again, Triple-A not included.)

Highest Isos for top-100 Prospects (Min. 200 AB)

Biggest ISO underperformers among top-100 Prospects (min. 200 AB)