Hitter xwOBA Overperformers — May 4, 2021

Yesterday, I identified and discussed the hitters who have underperformed their xwOBA marks by the most significant margin. The list made for a good initial group of potential “buy at a discount” candidates. Today, we flip to the other end, those hitters most overperforming their xwOBA marks. The gaps here are much smaller than on the underperformer list. Once again, it is important to remember that xwOBA isn’t meant to be predictive, so don’t automatically assume these hitters will soon suffer a significant decline in wOBA to meet their xwOBA marks. Instead, it’s a backwards looking metric and would be better used to evaluate how the hitter should have performed. Just like I use SIERA instead of ERA in the early going to get an idea of how the pitcher has pitched, sans luck, I would lean toward using xwOBA instead of actual wOBA to evaluate how a hitter has performed.

This list is your initial “sell high” group. However, as mentioned in the comments of yesterday’s article, a hitter’s counting stats play a big role on whether his current owner is willing or able to sell at a discount or a premium. That’s why these lists are only a starting point.

Our biggest overperformer right now is Kris Bryant, as he rebounds from a disappointing 2020. What’s important to learn is that Bryant has actually outperformed his xwOBA every season in the league since his 2015 debut. From the BABIP reseach I did over the off-season, he’s one of the guys who has posted high BABIP marks and it’s been very difficult to determine how. So that’s one of the drivers of the consistent overperformance. At the moment, everything looks fairly normal for him pre-2020, with the exception of massive power. It’s anyone’s guess whether this will finally be the first year he posted a HR/FB rate over 20%, but it’s pretty clear that he’s completely back to normal. I therefore doubt it makes sense to sell him, but as always, it depends on the return you would get.

Remember when Byron Buxton was a potential big steals guy with some power? Yeah, he’s completely reversed that, becoming a power hitter with some steals. While duh, he’s overperforming with a .539 wOBA, a .470 xwWOBA is still ridiculous. His owners are now crossing their fingers he could manage to stay healthy all season. He’s only eclipsed 500 PAs once, and just barely, and that came back in 2017. His second highest PA total is just 331. If I were an owner, I’d fish around to see what I might be able to get for him. His plate discipline still stinks, he still swings and misses often, his BABIP is a crazy .451, and his HR/FB rate isn’t going to remain anywhere near 40%. So while he may have been so awesome to be deserving of this huge xwOBA, it doesn’t mean he’ll continue to hit the ball this hard all season.

Well gosh, would you have guessed that Randy Arozarena and his disappointing (to some) .332 wOBA has actually been super lucky so far, according to Statcast? It’s been a bizarre season so far for him as his strikeout rate has remained elevate despite solid marks in the minors, while he has stopped hitting liners and fly balls and bashing everything into the ground. But his .400 BABIP and 25% HR/FB are doing their best to overshadow his many other issues. I still have no idea what to make of him.

I wasn’t really on the J.D. Martinez rebound bandwagon because I was more worried about his health and back. As a 33-year-old, that’s typically something that doesn’t just go away. Oops. Clearly he’s healthy, so let’s pretend 2020 never happened. I wouldn’t sell.

The only rate you should care about for Jared Walsh is his strikeout rate, which improved significantly last year, and has remained below 20% so far this season. Sure, it’s jumped from last year’s big decline, but his current mark still represents far better than during his 2019 debut and his minor league marks from 2017-2019. Fewer strikeouts = more balls in the air that could fly over the fence for a dinger.

Mike Yastrzemski carried over his surprise 2019 with an even stronger follow-up last year, and looked to have continued the good results this year before landing on the IL. However, xwOBA tells us that he has declined significantly, even more than his lower wOBA suggests. That’s surprising considering his BABIP is already well down from the past two seasons. The key here is to turn that inflated strikeout rate around.

It shouldn’t be too surprising to find Yermin Mercedes on an overperformer list, but notice his xwOBA is still .403! Most of his underlying skills look like a reasonable bet to be maintained, except his BABIP, which has no chance of finishing over .400. That’s likely where the overperformance comes from. I wonder how quickly he loses playing time when he hits a BABIP slump for a week or two, even if his wOBA might remain in the high .300 range. I doubt anyone is buying here, so as an owner, might as well keep him in your Util slot until he hits that BABIP slump and loses the playing time.