Muscling Up: ISO Surgers

Recently I’ve taken a look at early season changes in contact rate and fly ball rate because of Russell Carleton’s research showing we’ve reached the point in the season where the sample for those statistics has become ‘reliable.’ There has been some debate in the comments about what reliable means and how much the small season sample can help us in predicting what a player will do the rest of the season.

I look at it like this. For the statistics that have crossed that reliability threshold,  we can look at the players who have seen the biggest changes in either direction and feel safe that their skill has improved or decreased to some degree. That doesn’t mean regression isn’t coming. It just means that at the end of the year it wouldn’t be a surprise to see a player with an improvement or decline from their career mark in a particular category. Although the improvement or decline at the end of the year is not likely to be as extreme as it is at this point in the season.

Today I want to look at the hitters who have seen the biggest changes in ISO because a fair number of players have now crossed the 160 AB threshhold shown in Carleton’s research. Below are the guys who have seen the biggest increase in ISO. After that, we’ll examine whether some other statistics back up the power surge. And a little bit later we’ll see if we can’t figure out how much regression to expect.


The first thing that jumps out at you when you look at this list of names is the overall youth. Of the ten, eight are 27 or younger, and Daniel Murphy and Shin-Soo Choo are the oldest at only 28 and 30, respectively. Choo has the switch from Cleveland to Cincinnati going for him as Cincy is about 6% more homer friendly for lefties than Cleveland is.

I also took a look at whether these guys had seen an increase in average HR and fly ball distance over at Below are the results.

 Distance Gap

This largely backs up the increases in ISO with all but one in the sample seeing an increase. It’s especially encouraging for Justin Upton and Chris Davis given that they have seen the biggest ISO increases. Carlos Gonzalez’s ISO increase seems bit fluky according to this data. However, his average line drive and ground ball distance is up about 24 feet. And home runs aren’t the only component of ISO. Doubles and triples count as well. Cargo is hitting doubles once every 16.67 PAs this year compared to once every 18.67 PAs last year.

The next question is how much regression should we expect? With the help of Jeff Zimmerman’s, Mike Podhorzer and Chad Young did a five part series on predicting HR/FB rate here on the site. You should absolutely check it out. It’s phenomenal work. And I’m assuming most of you have seen it. They found that there is a strong correlation between the average distance of batted balls and HR/FB.

They then took the study much further and I honestly don’t have the ability to use their formulas. For my simple purposes of trying to identify over and undervalued fantasy players, I’m just going to use average HR and fly ball distance to compute some sort of expected HR/FB rate. Below is a graph showing the relationship between the two for the hitters with 160+ PA this year.


Denard span had the lowest average HR and fly ball distance at 246.53 feet. Paul Goldschmidt is tops at 315.73 feet. That’s a range of 69.2 feet. The slope of that trendline is 0.003238 meaning for every extra foot within that range the HR/FB% increases by .003238. So if we multiply the slope and the distance each hitter is above that 246.53 foot minimum, we can get an expected HR/FB (xHR/FB%). Again, I realize this is a more than imperfect way of doing this. But I’m just trying to get a general idea of who has the most regression coming, and this is a decent enough way to serve that purpose.

 xHR-FB Gap

Both Upton and Choo have a gap between their HR/FB and my version of xHR/FB that is more than two standard deviations away from the mean.  Maybe you should consider dealing them for hitters who are more capable of sustaining higher HR/FB rates.

Of the two, I’d be more inclined to deal Upton for two reasons. First, the gap between the perceived value of Upton and Choo is much larger than the actual gap between the two. You can get more for Upton. Second, Choo is more of a multi-category contributor. Upton’s average is just that, average, and he has only attempted three steals so far (all successful). Meanwhile, Choo is a solid four category contributor.

Davis, Goldschmidt and Gonzalez seem like possible targets. Goldy and Cargo are five-category contributors. If power is your biggest need, Davis is an attractive option. And if you dealt Upton for Davis or Goldschmidt, there’s a possibility you could add an extra piece on each side in which you would have the advantage to make up for the loss in draft day value. Maybe that’s a reach, but it’s worth a shot.

As for the other guys, this little exercise has sold me on Mitch Moreland and Josh Donaldson having some staying power. I wouldn’t be looking to sell them. We all suspected Anthony Rizzo was for real. Brandon Crawford’s power is sure to regress, but who is buying him? And Murphy is fine to hold on to if you’re using him at middle infield.

Long story short? I would not have a problem trading Upton.

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23 Responses to “Muscling Up: ISO Surgers”

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  1. John says:

    I’ve actually been talking about dealing Upton for Goldy in my league. We count OBP and SLG. as well as the standard R, HR, SB, RBI and AVG. Would you take Goldy straight up in that deal if you couldn’t get more? It’s a permanent keeper league as well. No penalty for keepers longterm. Who gets the edge in that format? Thanks.

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  2. John says:

    Also, completely unrelated, but can I drop Moustakas even in a longterm keeper like this? I’ve already had him benched for a few weeks.

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  3. rustydude says:

    Great piece. Another reason not to expect too much regression from Chris Davis is how he was hitting during his one “slump” of the season. He got off to a super hot streak to begin the season, and now he’s on his 2nd hot streak, with lots of homers in each. But if you look at the relative dry period from April 12 to May 8th, where he only hit 3 HR’s in 3.5 weeks, his triple slash was still .275/.381/.463. He still hit 6 doubles during this period and he walked 14 times during this period vs 10 times during the hot streaks (roughly the same # of PA’s during “slump” and hot streaks).

    Of course, his next slump could be worse, but we’re fast approaching 3 consecutive regular season months of incredible production from Davis, dating back to September of last year. He’s looking like the real deal.

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  4. Pauly says:

    was the ISO of Upton’s 2012 encompassing the entire season? I’m assuming so…
    if that’s the case i’m not sure that’s totally fair as he’s the only guy on that list that wasn’t healthy for a good part of last year. he’s also coming into his prime, 26 this year, so the jump to me isn’t that surprising.

    i will agree from a fantasy standpoint that upton’s value is purely power now. he’s not hitting for avg and being on an all-or-nothing braves team, there’s really zero reason for him to steal or for the braves to play small ball.

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    • Dan says:

      Upton is hitting .273, which I believe is actually above average this year. His Babip (.300) is below his career average of .333; there could be a little bit of positive regression for Upton in the BA category. Also, something seems amiss with Upton’s Fly Ball + HR distance–his average HR has traveled a “True Distance” of just over 427 feet. Maybe there are IFFBs in there skewing the data?

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  5. Stuck in a Slump says:

    Something that I’ve noticed here that really irks me is when Fangraphs points out that Choo will/is doing better in Cincy because of the left handed HR inflation vs Cleveland. The truth is that he’s going the opposite way when he hits doubles 7/2/2, his HR spray chart sits at 3/2/4, and his triple slash spray chart is .468/.468/.851 to left, .450/.450/.650 to center and .275/.275/.625.

    This tells us what we’ve known for a while now: Choo hits like a righty.

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  6. Jordan says:

    Of note: Bryce Harper’s ISO has increased from .206 last year to .324 this year, but only having 164 PA, he does not qualify for the 160 AB mark yet. His average HR+FB distance is up to 313.291 this year from 280.839 last year. I didn’t bother to put that graph together but i’m estimating his xHR/FB% at 21.6%, with his actual HR/FB% being 30.8% for a gap of roughly 9%.

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  7. emrldwpn says:

    Where is Bryce Harper? His ISO has increased from .206 to .324, or an increase of .118, which would put him third on the list. He hasn’t reached 160 AB yet, but he is close enough that not even mentioning him seems like a huge oversight.

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  8. Dingbat says:

    Maybe I’m missing something, but it looks like something went wrong with your xHR/FB calculations. If Goldschmidt is the top dot in the graph with 315.73 ft, then he’s well above the trendline, meaning that his expected HR/FB should actually be higher than it is. When you calculate his xHR/FB, however, you get a lower value. Looking at the graph, it doesn’t seem right that Goldy should have an HR&FB distance of 315.73 ft and an HR/FB rate of 22.41%.

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    • Brett Talley says:

      Yeah you’re absolutely right. I did the work on my home computer and I’m at work right now so I can’t look at the spreadsheet I used. But I’m guessing the mistake came when I was trying to pull names and numbers from my main list to put in order for the published chart. I’m guessing it had something to do with the formulas I had in the original cell not “copy and pasting” right. Good spot.

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      • donut says:

        You have the variables flipped. Distance should be on the x axis.

        Also, logically distance vs HR/FB should be exponential rather than linear. If your average batted ball distance is 250 vs 275 feet it really doesn’t matter since not many are leaving the yard either way. If it’s 300 vs 325 feet, that’s a big difference. Probably 10% or more on HR/FB

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  9. jfree says:

    Not sure why the change in ISO is supposed to be more correlated with y/y change in FB distance than in absolute FB distance. Specifically re CarGo, it appears to me that last year was more of a fluky low ISO than this year is.

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  10. deezy333 says:

    What’s your take on Heywards ISO? Obviously his BA is deflated by a horrible BABIP, but the rest of his stats look solid, including an improved bb%, k%, swk%, fb%, and ld%. However his ISO is way down. Any thoughts?

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  11. Jon L. says:

    I think Upton’s slugging percentage is now not even .400 over the last 3-4 weeks – about as long a time as it was crazy high. The performance has already regressed, even if the overall numbers haven’t.

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  12. lee says:

    wait a minute, why is the expected HR/FB% dependent on other players?
    You’re basically saying that we should expect fewer HR from Upton because Denard Span barely hits any.

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