Keston Hiura Versus the Regression Monster
Keston Hiura hit 38 home runs last year. There are qualifications to that statement, sure — 19 of those home runs came in the homer-happy PCL, and the majors weren’t much better when it came to mass dingerization. But still — Keston Hiura, who hit 13 home runs in 535 plate appearances in 2018, hit 38 home runs in 2019. What did he do to become such a great power hitter, and should we expect to see it again in 2020?
The first place you’d generally look, when considering an outlandish result like this, is for something wildly unsustainable. Maybe he turned half of his fly balls into home runs, and we can just point at that and move on. Indeed, Hiura’s HR/FB% was a juicy 24.1% in the majors last season, and an even more preposterous 36.5% in Triple-A.
Let’s throw out the Triple-A numbers for now. The combination of a new stadium in San Antonio and a wildly changed offensive environment makes putting those home runs into context difficult, so we’ll simply focus on the major league numbers. Non-pitchers hit home runs on 15.4% of their fly balls in 2019. Lower Hiura’s 24.1% to average, and he would have lost out on seven home runs. Easy peasy, let’s get lunch… right?
Well, yeah, not so much. I prefer to look at a different denominator: balls hit with between 15 and 45 degrees of launch angle rather than “fly balls.” That adds some line drives, which are potential home runs, and removes balls hit at too high of an angle to get out. Hiura had 83 of those in 2019, and turned 22.9% of them into homers. The league turned roughly 15% of theirs into dingers. Still the same seven home runs.
But batters aren’t all average. They have control over their home run rates, far more so than pitchers. Regress Hiura’s results in 2019 back towards the mean, and they suggest a true talent home run rate around 20.5%. That would still give him 17 home runs in the majors, not too much worse than his actual production. Read the rest of this entry »
