Hitter xwOBA Overperformers — May 4, 2021, A Review

Yesterday, I reviewed the list of hitters who most underperformed their xwOBA marks through May 1. All but two of the 11, who had already posted actual wOBA marks over .400, improved their wOBA marks over the rest of the season, some quite dramatically. Let’s now review the hitters who most overperformed their xwOBA marks through May 2 and find out how many of them did indeed suffer a wOBA decline through the rest of the season.

Like on the underperformer list, nine of the 11 hitters here did suffer a wOBA decline over the rest of the season (last column highlighted in red). It was a combination of both ISO and BABIP drops that fueled the wOBA slide. Six hitters, which is just more than half, actually posted wOBA declines of at least .100, which is quite significant. It resulted in an aggregate rest of season wOBA that was well below their xwOBA marks during the first month.

Kris Bryant has outperformed his xwOBA every single season of his career! I’ve tried to figure out why and made some progress in the past, but still can’t explain his consistently strong BABIP marks (except 2020). This year, his wOBA tumbled after the first month, as his ISO was more than cut in half and BABIP heavily regressed. Though unrelated to his wOBA and xwOBA, I remain surprised that he has never posted a 20% HR/FB rate given his big power output in the minors. He’s certainly been an excellent MLB hitter, but hasn’t peaked at quite the level of power I think many figured he would.

Byron Buxton was so fire that first month, even his xwOBA was ridiculous. Sure, he regressed over the rest of the season while he wasn’t on the IL, but was still fantastic. His ISO went from other-worldly to merely elite, but his BABIP also went from insanely good to simply league average. Given his crazy injury history, he’s the ultimate high risk, high reward guy.

After last year’s small sample regular season and postseason heroics, Randy Arozarena was one of the hitters I was most curious about this year, and I’m sure many felt the same way. Surely he couldn’t replicate those efforts, but he couldn’t totally fluke his way into such a performance, right? Welp, maybe he kinda did, as his HR/FB rate and ISO fell right back down to where his minor league record suggested, as if his 2020 MLB performance never happened. Anyhow, he was one of just two who actually increased his wOBA over the rest of the season, thanks partly to a rebound in ISO, offset somewhat by a decline in BABIP. Given his power/speed mix, I’m not sure how I’ll handle him as the fantasy upside remains, but he massively outperformed his xwOBA, which increases his risk.

After a massively disappointing 2020, J.D. Martinez went bonkers to open the season. While no one expected him to keep up that kind of pace, it certainly gave his owners the confidence to believe a complete rebound was in the works. Unfortunately, that didn’t really happen. Both his ISO and BABIP tumbled after the first month and while he finished as a pretty solid fantasy contributor, he still fell far short of his peak years in 2015 and 2017-2019.

Obviously, there was no way Jared Walsh was maintaining a BABIP near .400 all season. That fell significantly after the first month and brought his wOBA down with it. He still ended up a solid contributor, though his strikeout rate nearly double from his small sample 2020 mark.

Thanks to declines in both ISO and BABIP, Xander Bogaerts ended up posting a rest of season wOBA just above his first month xwOBA. This ended up being his lowest ISO and HR/FB rates since 2017. It’s possible his 2019 proves to be the best offensive season of his career and peak home run total.

Mike Yastrzemski wasn’t even that good over the first month, but xwOBA thought he should have been a whole lot worse! Luckily, he ended up ever so slightly better over the rest of the season, even though both his ISO and BABIP declined. A BABIP collapse was mostly what was behind his performance decline, but as a left-hander and extreme fly ball hitter, I’d be his true talent level is closer to his 2021 BABIP than 2020 BABIP.

Here’s to hoping 2022 will be a return to health and elite performance for Mike Trout.

Sure Jesse Winker couldn’t maintain a .458 wOBA all season, but he was still awesome all year, posting a .392 mark the rest of the way. That’s pretty incredible considering his BABIP plunged from .424 to just .302. The encouraging thing here is that his strikeout rate fully rebounded after his small sample 2020 spike. He remains an OBP league monster, though he still hasn’t recorded 500 PAs in a season yet.

Yermin Mercedes was one of the first month’s biggest surprises, which likely made it hard for his lucky owners to sell high. He endured a complete collapse, going from elite hitter to minor leaguer, as his power disappeared and BABIP fell back to Earth.

Austin Riley barely lost a step over the rest of the season, as a drop in BABIP was compensated by a surge in ISO. While the power looks pretty real, it’s hard to believe the .368 season BABIP is.