Hitter xISO Underperformers & Overperformers

Usually this early in the season, I would share the xwOBA under/overperformers. However, a suppressed or inflated BABIP has a dramatic impact on the gap between wOBA and xwOBA and since we remain in small sample size territory for the metric, I didn’t want to include a list of obvious names. We all assume a sub-.200 BABIP is going to rebound! Likewise, a .450 BABIP isn’t sustainable. So instead, let’s review ISO versus xISO.

Of course, this isn’t actually a metric that’s directly calculated. But, it’s easy to do it yourself, as it’s just SLG – BA for ISO and xSLG – xBA for xISO on the Statcast Expected Statistics Leaderboard page.

Let’s start with the xISO underperformers, who you might expect to increase their actual ISO marks over the rest of the season, assuming stable underlying skills.

Wow, that’s a big number for Salvador Perez! Obviously, there’s little chance he actually records an ISO that high, though he did finish with an elite .271 mark back in 2021. It seems really, really hard to post just a .127 ISO, while also posting an elite 18.3% Barrel%. The HardHit% is also strong, while he has maintained a mid-40% FB%. Ignore his age, as this is not the beginning of a decline. He’s a prime “hot streak imminent” candidate.

Gosh, Matt Olson disappointed last season after a monster 2023, and once again he’s off to a weak start. The lack of power output makes even less sense than it does for Perez above, as he has posted an absurd 62% HardHit%, which ranks sixth best among 172 qualified batters. Everything looks great here, except the one really odd thing is a sudden penchant for grounders. His batted ball distribution is suddenly low on flies and liners, and heavy on worm killers, so not sure what’s going on there. But given last year’s performance, his owner might be getting worried a big rebound ain’t in store, making him a great trade target.

Ryan Jeffers has yet to homer, and his Statcast metrics don’t look nearly as exciting as the above two. Here, his Barrel% is actually down to the mid-single digits and has actually declined every single season since 2021. I wouldn’t worry though as it’s been just 45 ABs. I wouldn’t value him any differently than I did before the season began.

It’s surprising to see Brandon Lowe’s name here, as his HR/FB rate is in line with his history, though his FB% is down a bit into the mid-30% range after six straight seasons above 40%. The answer is a bizarre zero doubles. With no triples, that means his only extra-base hits have come from his three homers! Everything looks normal here and some of his line drives will likely turn into fly balls to get his batted ball profile in line with career marks.

A slow start from Yordan Alvarez?! His HardHit% is down a bit, but still strong, while his Barrel% is in line with last year. A jump in strikeout rate has no effect here, but it’s something to monitor if you’re an owner. I don’t see any reason not to expect a full rebound here (and as an owner of him in two of three leagues, he better rebound or my teams are toast!).

It’s kind of hilarious to see Shohei Ohtani’s name on here given that he already owns a .263 ISO. His xISO is an off-the-charts .390! That’s quite surprising considering his HardHit% is just barely above last year, while his Barrel% is lower than his marks the last two years. Whatever, he’s good.

I love how Dylan Crews hit two home runs the day I wrote this article, so he’s going to fall off this list. All he needed was a visit to Coors Field to get rid of that zero by his home run total. The Statcast numbers here, before the two dingers, weren’t very impressive, as evidenced by his mere .124 xISO, but it was still good enough to make the list because he had recorded a big fat zero extra-base hits before the outburst.

Max Muncy with just a .065 ISO?!?! He somehow hasn’t homered yet, despite the highest HardHit% of his career and a Barrel% in double digits. Hurting a bit here is a severe drop in FB% to the mid-30% range as he’s been around 50% the last three years. The obvious explanation here is a huge spike in LD%, which won’t last, and many of those liners will become fly balls. I might get concerned about the elevated strikeout rate, but aside from that, he’s fine.

Now let’s flip over to the overperformers.

Cedric Mullins’ HardHhit% is stable and his maxEV is in line with past years, but his Barrel% is sitting at a career best. So there has been some improvement, and he’s been aided by a career high FB% that has jumped over 50% for the first time. But his xISO suggests this is the same hitter he’s been all these years, so the results ain’t going to last.

Jake Cronenworth is currently on the IL, so it’s going to be impossible to take advantage of his start. Somehow, his HR/FB rate is sitting at a career high, despite a career low Barrel%. The sample size here is tiny though, thanks to the injury, so this analysis is pretty meaningless.

Did anyone think Matt Mervis was en route to a huge breakout year after being traded to the Marlins? His stat line is quite comical actually. He has posted an insane 50% HR/FB rate, and although that’s obviously not sustainable, he has also posted an elite 60% HardHit% and 20% barrel%. But that has also come with a 43.1% strikeout rate and 21.7% SwStk%. Is he selling out for power, closing his eyes and swinging as hard as he can? Perhaps!

Jung Hoo Lee figured to contribute a little of this and a little of that, with a strong batting average. Instead, he’s knocked three homers already with an ISO approaching .300! Whaaaaat?!?! His HardHit% is actually decent and he’s nearly doubled his Barrel% from last year to sit right around league average, but a 104.5 MPH maxEV suggests he hasn’t actually increased his power. I definitely don’t think this start hints at a 20-homer season.

José Ramírez is such an odd power hitter. His Barrel% marks are routinely league average or worse, his career HR/FB rate is around the league average, perhaps slightly higher, as is his HardHit%. Yet, a strong strikeout rate and extreme flyball tendency have resulted in high home run counts, including two 39-dinger seasons. He’s a big pulled flyball guy, so it’s likely xISO is underrating him here. That said, his HardHit% sits at the lowest since 2015, while his Barrel% remains unimpressive. I think there’s a real chance he disappoints this year, especially coming off one of his most valuable fantasy seasons.

So much for the worry that Mookie Betts’ illness causing him to lose weight would reduce his power output! Then again, the Statcast metrics are ugly. His HardHit%, maxEV, and Barrel% are all sitting at career worsts, with the latter two marks scarily low. Like, you’d never guess Betts has posted these marks. I’m not sure how to evaluate what he’s done because it would made sense if he got off to a slow power start. However, the metrics suggest the results should actually represent a slow start, but that hasn’t been the case. So maybe he’s just been very fortunate and he’ll slow down from here, or perhaps he’ll get healthy and the underlying skills will catch up to the results.