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Toolshed: ISO-lating prospect power

Comparing MiLB production to expectations in terms of slugging
November 13, 2015

Here's the thing about what are considered advanced stats. Some of them aren't really advanced at all, other than that they're a little beyond the traditional batting average, home runs, RBIs, ERA, win-loss record, etc. 

Take ISO, for instance. ISO is short for isolated slugging percentage. All that means is ISO is the statistical difference between a player's slugging percentage and his batting average. Nothing more than that. You just subtract the AVG from the SLG and you get ISO. It's a nice way of seeing who packs the most punch when they make contact. After all, average only tells us how many times a player got a hit, and slugging percentage is dependent on hits as well. If you want to look at pure power, ISO is a good non-home run place to start.

To give you an idea of what a good ISO looks like, Bryce Harper (.319), Chris Davis (.300), Mike Trout (.290), Nolan Arenado (.287) and Jose Bautista (.285) finished in the top five in the Majors for ISO this season. No particular surprises there if you think about the Majors' most powerful sluggers (and the fact that Arenado plays in Colorado). 

But what about the best prospects in the game? How much pop did they show in the Minors in 2015?

Highest Isos for top-100 Prospects
6 Joey Gallo (TEX) 3B/OF 321 77 .240 167 .520 .280
91 A.J. Reed (HOU) 1B 523 178 .340 320 .612 .272
65 Lewis Brinson (TEX) OF 398 132 .332 239 .601 .269
62 Andrew Benintendi (BOS) OF 198 62 .313 110 .556 .242
50 Ryan McMahon (COL) 3B 496 149 .300 258 0.520 .220

(All numbers are from the Minors only and were rounded to one decimal place to fit the table. As a result, some differences reflect the subtraction of the raw data.)

The first thing that stuck out to me was how much power was down among Top-100 prospects in 2015 as compared to 2014. Gallo's .280 ISO wouldn't have even fit in the top five last year, when Jorge Soler stood at the top with an eye-popping .360. The easy reason for this, of course, is the fact that the three Cubs prospects who placed in the top five a year ago (Soler, Kris Bryant, Kyle Schwarber) have since graduated from prospect lists and took their power to great heights on the North Side of Chicago. Gallo's number dropped from .344 to .280 as he saw tougher competition at Triple-A Round Rock. In fact, the average ISO among Top-100 prospects dropped from .182 in 2014 to .150 in 2015, but again that correlates to a drop in talent pool as the average power tool among Top-100 prospects went from 53.9 to 51.0. But more on power tools later. 

As for this year's group, Gallo, despite the dropoff, remained a king of ISO. The 21-year-old slugger may have been limited to a .240 average between Double-A and Triple-A this season -- due to a 37.2 percent strikeout rate -- but when he did make contact, it was loud. Forty-three of his 77 hits in the Minors went for extra bases.

Reed's inclusion is no surprise to anyone who followed his season. The guy led full-season Minor Leaguers in slugging percentage, OPS, total bases and home runs. If he wasn't somehow in the top five here, we'd have to reconsider ISO as a stat. Same goes for Brinson, who had 59 extra-base hits across three levels and was one of three full-season Minor Leaguers with an OPS above 1.000. 

On the surface, Benintendi -- the first-round Red Six pick who is listed at 5-foot-10, 170 pounds -- might be a surprise, but not when you consider he hit 11 homers in 54 games at the lower levels of the Boston system. At just 198 at-bats, he has the smallest sample of this year's group of five, but considering he went deep 20 times as a Golden Spikes-winning sophomore at Arkansas in the spring, you should consider Benintendi's power quite real.

Rounding out the group is 20-year-old McMahon, who hit 18 homers, six triples and 43 doubles at Class A Advanced Modesto. If you think most of that power came from playing in the offense-rich California League, you'd be only about half right. The left-handed slugger made his home in Modesto, which is one of the least homer-friendly parks in the Cal League, and as such saw 15 of his 18 blasts come on the road. He'll see fairer and tougher competition in a big test at Double-A Tulsa next season, but for now, McMahon and the Rockies should be happy with his second straight season of posting a .220 ISO. 

lowest Isos for top-100 Prospects
53 Daz Cameron (HOU) OF 175 44 .251 54 .309 .057
82 Amed Rosario (NYM) SS 395 100 .253 130 .329 .076
77 Nick Gordon (MIN) SS 481 133 .277 173 .360 .083
24 Jose Peraza (LAD/ATL) 2B 481 141 .293 182 .378 .085
29 Gleyber Torres (CHC) SS 487 140 .287 183 .376 .088

First things first, it's no surprise that we have some repeat customers from last year's list. Gordon showed his .072 ISO in his Draft year of 2014 wasn't just a small-sample mirage. He still has plus speed and impressive enough defensive skills to make him a Top-100 prospect, but he did fall from No. 33 before the season began to his current spot at No. 77 because of his offensive limitations. In that same vein, Peraza had the fourth-lowest ISO among top prospects a year ago and is back there for 2015. The 21-year-old, who was dealt to the Dodgers around the trade deadline and made his Major League debut with Los Angeles on Aug. 10, can still hit for a decently high average and steal a ton of bases (157 over the past three Minor League seasons), so he'll enter 2016 Spring Training as a candidate to replace free agent Howie Kendrick at second, barring any major moves by the Dodgers.

As for the newcomers, Cameron didn't show much pop after being taken by the Astros with the 37th pick in this year's Draft. Only seven of his 44 hits between the Rookie-level Gulf Coast League and Greeneville went for extra bases, and none of those were home runs. Is that something to worry about? Not at all. Yet. Anything the 18-year-old outfielder would have done in the pros after a full spring of high-school ball would have been gravy. Give him a full offseason to prepare for a full season of pro ball, and check in then. The Astros certainly aren't worried.

The same can be said of the Mets and Cubs when it comes to Rosario and Torres. Rosario played the entire season as a 19-year-old in the Class A Advanced Florida State League, where power goes to die, and didn't homer in 103 games. Average power might come to the Dominican Republic native some day, but it won't happen until he matures physcially and plays in more offensive-friendly environs. Torres was in a similar spot in the Class A Midwest League at just 18. Once he catches up to his competition in age, average power should develop.

Expectations vs. performance

We've tapped into it a little bit so far, but here's the point in which we put ISO into context.

Because we're dealing with prospects here, we're able to use's scouting grades, which are used on a 20-80 scale and are typically used to project future Major League skill, to measure how these players stacked up against what is expected of them. For example, Gallo is considered an elite 80-grade power hitter, so the fact that he leads this group of top prospects in ISO should come as no surprise. 

We're able to use average and standard deviation to get ISO and scouting grades on similar scales. The average for ISO was .150 with a standard deviation of .0487, and the average power tool grade was 51.0 with a standard deviation of 10.12. In other words, roughly 67 percent of the tool grades fell between 40.88 and 62.12. (Of course, tool grades are usually in multiples of five, but you see what we're getting at.)

So with those in hand, we can compare how prospects held up to their power tool grades. Any positive difference between ISO standard deviation and grade standard deviation means the prospect outperformed our expectations. Any negative difference means they underpeformed. Anything close to zero is a solid "meets expectations."

Let's look at both ends of the spectrum:

Biggest ISO overperformers among top-100 Prospects
MLB.COM RANK NAME POS ISO Power Grade ISO STD Grade STD Difference
30 Ozhaino Albies (ATL) SS .094 20 -1.2 -3.1 1.9
91 A.J. Reed (HOU) 1B .272 60 2.5 0.9 1.6
65 Lewis Brinson (TEX) OF .269 60 2.4 0.9 1.6
12 Orlando Arcia (MIL) SS .146 35 -0.1 -1.6 1.5
62 Andrew Benintendi (BOS) OF .242 55 1.9 0.4 1.5
10 Dansby Swanson (ARI) SS .193 45 0.9 -0.6 1.5

Albies had such a low bar to clear, given that he has the lowest possible power grade, that any type of power at all would make him look like an overperformer. Although he didn't homer in his first full season at Class A Rome, the Braves' top prospect did double 21 times and triple eight times -- numbers that were undoubtedly helped some by his 70-grade speed as he tried to grab an extra base here and there. His ISO showed he performed more like a 40-grade power hitter, so still not anything to write home about, but still leaps and bounds above a powerless 20-grade power guy.

On the other side of the coin, Reed and Brinson should someday make good, if not great, power hitters given their skill sets, but in 2015, they played like elite talents as far as that tool goes. Both were given above-average 60 grades by in the middle of the season, but played more like 75-grade sluggers by the time the season was over. Of the two, Reed's power seems like it's much more real and sustainable, given his build and his ability to crush Double-A pitching over a sustained time, while Brinson did most of his bashing at Class A Advanced High Desert, which is known to be a boon for hitters. Brinson, to his credit, handled Double-A and Triple-A pitching well in small samples, and he'll get a chance to show just how real his power is away from the Cal League at the upper levels in 2016.

Arcia's power jump was discussed in length in our MiLBY story naming him the Breakout Prospect of the Year, but he's featured here because he doubled his home runs from four in 2014 to eight in 2015 and collected career highs in triples (seven) and doubles (37). The long and the short of it: Arcia's strength matured in a big way in 2015, and although he'll never be a big-time power guy, don't be surprised to see his power grade tick up when reports come out this winter.

It'll be interesting to see whether the industry starts to change its views on Benintendi's power this offseason. As previously mentioned, he showed plenty of pop in college, but there were concerns that it wouldn't translate once he got a wood bat in his hands. Well, it certainly did in his first pro season as the Red Sox saw fit to move him to Class A Greenville -- a move they don't typically make with players during their Draft years. In a previous Toolshed, Arkansas coach Dave Van Horn said the wiry 5-foot-10 outfielder added plenty of strength between his freshman and sophomore years, and though it didn't result in a much bigger figure, it did result in some big-time power. You'll likely start seeing 60-plus when it comes to Benintendi's next power grade.

Although we wanted to keep it to five overperformers, we threw in Swanson because his standard deviation gulf was equal to that of fellow first-rounder Benintendi. Power is actually the top overall pick's worst tool, but with 11 extra-base hits in 83 at-bats at Class A Short Season Hillsboro, the D-backs can be happy with their introduction to the Vanderbilt product.

biggest iso underperformers among top-100 Prospects
MLB.COM RANK NAME POS ISO Power Grade ISO STD Grade STD Difference
53 Daz Cameron (HOU) OF .057 50 -1.9 -0.1 -1.8
93 Tyler Stephenson (CIN) C .093 55 -1.2 0.4 -1.6
14 Nomar Mazara (TEX) OF .147 65 -0.1 1.4 -1.4
31 Josh Bell (PIT) 1B .129 60 -0.4 0.9 -1.3
56 Kyle Tucker (HOU) OF .108 55 -0.9 0.4 -1.3

What we said above about Cameron applies to Tucker (this year's fifth overall pick) and Stephenson (11th overall) as well. The day will likely come when all three can show off average to slightly above-average power, but it's not going to happen necessarily in their introduction to the pro game after a long spring season. Give the kids time.

Though he may be more advanced than the other three, Mazara is also worthy of your patience. At 6-foot-4 with good strength, he certainly looks the part of a player who will grow into becoming a big-time slugger, leading to his 65 future power grade tool. Actually, the fact that he performed like an average 50-grade power hitter, despite being a 20-year-old in Double-A, is more of a point in his favor than anything else.

As for Bell, it might be time to start thinking that he won't be much of a slugging first baseman once he hits the bigs, likely next season. The Pirates' No. 3 prospect hasn't hit more than 13 homers in a season, and that came at Class A West Virginia in 2013. As a switch-hitter, he has plenty of other offensive tools in his bag, as evidenced by his .317 average and .393 OBP between Double-A and Triple-A in 2015, but it's tough to project him as being anything more than a 15-20 homer guy in the Majors, even once he matures fully.

Other ISO notes

  • The three players to meet their power expectations perfectly evenly were Byron Buxton, Corey Seager -- the two top prospects in the game -- and Aaron Judge. Those first two already have Major League experience and should be in "The Show" on Opening Day while Judge will likely work his way there at some point, especially if and when he improves on his .224/.308/.373 line in 61 games at Triple-A.
  • Back in June, Bradley Zimmer was featured in Toolshed as a player who was beating expectations for both power and speed. At the time, he was considered to have 50-grade power. The team ticked that up to 60 once he did so well in the season's first half, and now with the season over, it appears that he slightly underperformed once the goal posts were moved on him. A litle extra context on that -- the Indians' top prospect struggled down the stretch at Double-A Akron, and it looks like that was due to a hairline fracture in his right foot.
  • A reminder that if a player did "underperform" his expected ISO in 2015, that doesn't mean he can't bounce back the following season. Carlos Correa was in our five biggest underperformers for ISO in 2014 and did nothing more than become one of the game's most exciting talents. His ISO in the Majors, by the way? .233. 



Sam Dykstra is a reporter for Follow and interact with him on Twitter, @SamDykstraMiLB.