2018 May Isolated Slugging Decliners

Yesterday, I used the Statcast expected metrics to calculate player xISO marks, then comparing them to actuals. I began by looking at those hitters who have posted ISO marks most below their xISO marks, suggesting the potential for significant upside in the near future. Today, let’s discuss hitters whose actual ISO marks have most exceeded their xISO marks, suggesting possible downside.

Didi Gregorius has been one of the season’s biggest surprises so far, with all his underlying metrics supporting a big breakout. But xISO isn’t totally buying it. However, do note that his xISO stands at .231, which would still easily represent a career high. So Statcast agrees he’s been better than ever before, but not nearly as good as his current results. And regression already has been catching up with him — his wOBA during his absurd first month of the season stood at .465, but has collapsed to just .148 in May. He also has yet to homer in the month, after launching 10 in April.

Also concerning is that his walk rate, which was about triple his previous marks during April (another strong signal this is a real breakout), has declined right back to where he always was at 5.9%. You can’t sell high any longer given his May performance, so owners probably have no choice but to hold and hope he looks closer to April than May the rest of the way. Also remember that xISO ignores park factors. Yankee Stadium is one of the best parks for left-handed homers, and Gregorious has pulled 33% of his fly balls, a well above average mark.

Like Gregorious, Jose Ramirez may appear here, but it’s not really a call for impending doom. A .259 xISO is just below his big power breakout last season and he’s doing everything right. He has walked more than he has struck out, nudged his FB% above 40% and even stands to benefit from some more of his balls in play dropping for hits (that .254 BABIP is due to rise). Like Statcast, I wouldn’t bet on a HR/FB rate above 20% being maintained, but if it wasn’t obvious by now, his power spike last year was no fluke. As a five-category contributor, he’s a hold and enjoy.

Unlike the first two names, Jonathan Schoop’s xISO ain’t good. His actual ISO already sits at its lowest mark since his first full season in 2014, and Statcast is suggesting it should be even lower. His plate approach has always made me shy away, as he combines terrible plate discipline that includes swinging at everything and whiffing often, with far too many pop-ups. It puts his BABIP at risk of collapse and without any speed, you might end up with just a two-category guy.

Sooooo, Ozzie Albies is now tied for the league lead in homers after he knocked one out before I started typing this. Will the good times continue? He has now officially hit more homers than I projected for him all season! He’s never even posted a HR/FB rate in the double digits over his entire professional career before this. Where is this coming from?! Every time you think he’s due to cool down soon, he homers again. Obviously, the prudent decision would be to look into selling high. But I know his owners are unlikely to ever consider such a move. And even his xISO is .246, just a bit below double the mark I projected. So like the top two names here, Statcast is sorta behind this power, though not completely.

Kevin Pillar first enjoyed a marginal power breakout last season when his ISO spiked to a career high of .148. That still wasn’t all that good, but better than he’s done in the past. This year, he’s continued that growth, but xISO believes he’s actually not much different from last season. The funny thing is that he has just four homers, so even if his ISO declined to his xISO, you would have only lost like a homer. Who cares. You might note his impressive 32.3% LD% and think he can maintain a .349 BABIP, but the line drive rate itself is wholly unsustainable. That means he’s going to drop back into what we all expected to begin with, which includes mid-teen homers and steals. It’s still an underappreciated collection of stats.

Nolan Arenado’s appearance him is another reminder of xISO’s inability to account for home park. That said, surprisingly so far, only four of 14 Rockies hitters have overperformed their xISO marks. That’s in contract to last year, when 16 of 24 overperformed. Arenado did outperform last season, but by a lesser degree than he is currently. His overall skill set has changed significantly this year, as his walk rate has jumped into double digits for the first time, while his strikeout rate has skyrocketed. He has also hit a ton of line drives, but has popped up more often than ever. There’s nothing really actionable here though, but it’ll be interesting where these metrics move the rest of the way.