ISO-lating prospects' power in 2014

With Spring Training under way and Grapefruit and Cactus League games right around the corner, we're left with few relevant chances to look back on 2014 in an advanced stats way. After previously covering Fielding Independent Pitching, BABIP and Speed Score, this time we turn our attention to power -- more specifically, Isolated Slugging Percentage (ISO).

In terms of deriving the stat itself, ISO is perhaps the simplest one we've used so far. All you need to do is subtract a player's batting average from his slugging percentage. This gives us a number that looks purely at how powerful a player's hits truly are. In theory, a player could have a high batting average and a decent slugging percentage by only hitting singles. Therefore, if we looked at slugging percentage alone, we wouldn't get the whole picture. By using ISO, we focus solely on power and its role in a player's statistical profile.

But because we want to go a little deeper than just looking at ISO, (as with the previous feature on Speed Score) we've again included mean and standard deviation to determine how player's power performances stack up against expectations, using ISO and scouting grades. Before all that, let's just look at the leaderboard for the stat itself.

If anything could make Cubs fans even more excited about the future, it might be this table. The Cubs have six prospects in the top 100 heading into the 2015 season, and three of them are among last year's ISO leaders. Hamstring problems limited Soler to 62 games in the Minors (54 at either Double-A Tennessee or Triple-A Iowa), but when healthy, he showed why there's plenty of promise in his bat. If he were to maintain that pace over the same Minor League span as Bryant (594 plate appearances), he would have finished with roughly 38 homers and 101 extra-base hits.

What's more, he carried that powerful production to the Majors, where the Cuban outfielder batted .292 with a .573 slugging percentage for a .281 ISO over 24 games. The prospect talk going into this season revolves (for good reason) mostly around Bryant and when he'll get the call, but until he does, Soler should provide the North Siders with solid right-handed protection behind budding superstar Anthony Rizzo.

Although he's further away from the Majors than Soler or Bryant, Schwarber also has plenty of promise. The early returns were obviously great (.344/.428/.634, 18 homers in 72 games), albeit in the lower levels of the Cubs system. The left-handed slugger, who turns 22 in early March, only faces questions about his defense and whether he'll stick behind the plate or move full-time to the outfield, where he got a good chunk of time at Class A Advanced Daytona at the end of 2014.

Like Bryant, Gallo -- the only prospect given an 80 power grade by MLB.com this winter -- has been well-chronicled when it comes to his thunder, so his inclusion here is no surprise. The same can be said for Olson, who had 69 of his 134 hits (51.4 percent) go for extra bases in the hitter-friendly California League. Chances are those numbers will drop upon a move to Double-A Midland, where home runs are notoriously much harder to come by.

If you're going to be included in that table above and are still ranked in the top 100, it means you have something else going for you outside the realm of power, and that's mostly true for the guys above. McGuire and Hedges are both seen as plus defenders behind the plate -- more on both in Jake Seiner's recent piece -- while Gordon and Arcia get similarly positive grades at shortstop. Peraza, as we know, is a big-time burner on the basepaths, perhaps the best we've seen in the Minors since Billy Hamilton.

In other words, their profiles are all just fine.

If anyone on this list is a surprise, it may be McGuire, who provides an interesting case study. Since the Pirates drafted the left-handed-hitting catcher with the 14th overall pick out of high school in 2013, the word most associated with his power is "potential." As he gets older, McGuire is expected to have average power, but as his ISO shows, that just wasn't there in the South Atlantic League (18 extra-base hits in 98 games), where at 19 he was 2 1/2 years younger than the average player. That likely won't improve in the pitcher-friendly Florida State League this season, either, but given his youth, the Bucs will give McGuire plenty of time to develop at a natural pace. This is important to remember the next time power doesn't appear immediately for your favorite prospect.

Expectation vs. performance

Before we get started on the tables below, it's important to note that the power tool grades selected here are from the 2014 updated midseason lists. The new 2015 grades were taken into account after the performances, so we can't really call something created after the fact an "expectation." Yes, the 2014 grades were updated slightly in the middle of the season, but they are the best we have right now to correspond with expectations for this last season.

As with speed scores, we're using mean and standard deviation to weigh what scouts expect out of a player (grades) compared to their actual performance (ISO). A quick refresher: one standard deviation, both positively and negatively, from the mean (or average) gives us about two-thirds of the data. So the mean for power grades was 53.9 and the standard deviation was 11. That means roughly 67 percent of the grades given to the 52 position players used in the sample fall between 42.9 and 64.9. The ISO mean was .182 and the standard deviation there was .0663.

By focusing on mean and standard deviation, we put everything in the same unit measure and make it easier to compare grades with ISO. If the difference between standard deviations of ISO and grade is positive, then the player exceeded expectations; if it's negative, he underperformed. If it's zero or relatively close to it, he performed right where we thought he would.

Let's look at the extremes.

Soler was a 65 in terms of power by the middle of the season and has seen that number bump up to 70 this offseason. As explained above, that will happen when you perform like an 80-grade slugger.

The most interesting of the group might be Pederson at No. 2. During the outfielder's first three full seasons in the Dodgers system, he showed some nice power, topping out at 22 homers and a .219 ISO at Double-A Chattanooga in 2013. "Nice" power gets you a 55. What he did in 2014 was a lot more than nice. The 22-year-old left-handed slugger was named PCL MVP after hitting 33 homers and putting up a .279 ISO. (His .435 OBP and 30 steals helped him get the award, too, but we're focusing on power today.) Put another way, a 55-grade slugger performed like a 70-grader, even if he was aided by a hitter-friendly environment in Albuquerque, where he owned a .314 ISO. By September, Pederson was up with the big club, where he's expected to be the Opening Day center fielder after the trade of Matt Kemp. When MLB.com updated its rankings for 2015, Pederson, now the No. 12 prospect, had his power grade appropriately bumped up to 60.

Lamb was another guy who used a breakout in power to wedge himself into the Major League conversation. That power came mostly from doubles (39 in 108 games along with a career-best 15 homers), but his .240 ISO between Double-A Mobile and a brief stint at Triple-A Reno played more like a 65-grade slugger than the 50 he's received from MLB.com. The power didn't much carry to the Majors (.230/.263/.373, .143 ISO), and his return to the D-backs seems to have hit a roadblock with their signing of Cuban star Yasmany Tomas and the club's announcement that he'll likely play third base. It'll be up to Lamb to prove that his 2014 numbers in the Minors can be carried into the Majors if he's going to push Tomas back to the outfield.

Neither Anderson nor Margot had what would be considered standout power performances, but considering expectations were so low as 40-grade guys, the mere fact that they were average in terms of ISO puts them in the table up top.

That Franco appears here should be no surprise, even if ISO was a foreign concept before reading this. The Phillies prospect grabbed headlines as our Breakout Prospect of the Year in 2013 when he batted .320 with a .249 ISO and 31 home runs. Upon getting the call to Triple-A Lehigh Valley with a 70 power grade, the right-handed slugger struggled in the first half, batting .230 with a .134 ISO and only six homers in 87 games. Those numbers rebounded nicely to .309, .242 and 10 in 46 contests over the second half, but the first set of stats did enough to damage the whole picture. All the same, that second half helped Franco's power grade drop to only 65 and could help him take the Phillies starting third base job away from Cody Asche, depending on how his Spring Training goes.

Like McGuire, Frazier's elevated power grade when compared to production comes as a result of potential rather than current status. The Indians' 2013 first-rounder managed 13 homers in 120 games at Class A Lake County -- he also struck out 161 times -- but played the entire season as a 19-year-old. The power is expected to come with age.

The same can be said of Correa, who did pretty much everything at the plate before a broken fibula ended his season after 62 games. MLB.com's No. 3 overall prospect hit more like an average 50-grader than a 70-grader when it came to power at Class A Advanced Lancaster, but it's expected he'll continue to grow into that particular tool. If you've seen pictures of him this Spring Training, it seems like that growth may have already come.