Starting Pitcher GB% Surgers — Apr 21, 2021, A Review

Today, let’s move over to review early starting pitcher metrics and whether the surges or declines stuck around over the rest of the season. Unlike for hitters where depending on the type of hitter they are, the optimal batted ball profile is easier to determine, it’s not as straightforward for pitchers. So this isn’t necessarily a “good” list to be on, but it could change the shape of the pitcher’s performance. More grounders should result in fewer homers, but likely more hits allowed and a higher BABIP. So let’s get to the names of those that had increased their GB% by at least 10% through Apr 19 and see whether their GB% spikes were sustained.

Since I only listed six pitchers, this was more a mixed bag than the previous hitter lists, where the majority reverted right back to their historical levels. Here, two pitchers (Diff column highlighted) sustained enough of their early GB% spikes over the rest of the season to establish a new higher level. Another did maintain some of his increased GB% over the rest of the season, but not enough for me to get out the highlighter. Two more actually posted lower GB% marks than 2020 over the rest of the season, even after the early surge. And finally, another posted a minor increase the rest of the way versus 2020 and could essentially be called no change. So it was a true mixed bag and results in the same conclusion as for the hitters — early season metric changes over a small sample should be treated with a grain of salt. While the changes do stick for some, it’s likely impossible to tell which ones ahead of time.

An early season velocity surge (that didn’t last), along with this GB% spike, got me really intrigued by Casey Mize. He did end up holding onto a portion of those early season GB% gains and ended up posting the highest GB% of his professional career. Unfortunately, he’ll need to greatly improve his underlying skills, particularly his strikeout rate, to avoid serious luck regression as he handily outperformed his SIERA.

Steven Matz was the other pitcher on the list that held onto enough gains to experience a GB% spike all season long. However, this was more due to the career low mark he posted in 2020, which was the first time it dropped below 45.5%. It was a massive drop too, but it proved to be a small sample size fluke, as it happened over just 30.2 innings. Moving to St. Louis should be good for his ratios, though he’ll have to improve his underlying skills enough to avoid an ERA rise toward his less impressive SIERA.

Anthony DeSclafani was in a similar boat as Matz with 2020’s small sample resulting in a sub-40% GB%. He had done that once before, again over a small sample during his 2014 debut. DeSclafani dramatically outperformed his SIERA, though perhaps some of that will continue given his home park. Still, I ain’t paying for a low-3.00 ERA with a mediocre strikeout rate!

Germán Márquez failed to hold onto any of his gains and posted a GB% almost identical to his 2020 mark over the rest of the season. For a Rockies pitcher, more grounders are a good thing given the high rate of fly balls that leave the yard. Yes, it will hurt BABIP, but a single or double is still better than a home run. It would be quite exciting if he ever got out of Colorado.

Nathan Eovaldi was the only pitcher on this list that posted a GB% over the rest of the season that was significantly below his 2020 mark. As a result, he posted his lowest GB% since his 2011 debut. Instead, most of those former grounders became line drives, which is why he allowed a BABIP well above .300 once again. Luckily, his HR/FB rate slipped into single digits, so he ended up barely underperforming his SIERA. Can you believe that he had increased his strikeout rate for five straight seasons before a small decline this year?!

Did Corbin Burnes really need to limit his fly balls? He easily led baseball with the lowest HR/FB rate allowed among qualified pitchers, so his GB% this year didn’t matter a whole lot.