Statcast Pitcher Studs and Duds - HR/FB% Analysis for Week 8

May 18, 2021

Connelly Doan examines the Statcast leaderboard to identify pitchers whose rising and falling HR/FB% could make them worth adding or dropping in fantasy baseball for Week 8.

Welcome back to RotoBaller’s Statcast pitcher Studs and Duds article series! Each week I will select an advanced stat, choose two top performers and two under-performers, and analyze what those stats could mean for future fantasy output. The past several weeks I have looked at metrics that are more predictive. This week I will focus on one that is not entirely predictive on its surface, but can produce insights into certain aspects of a pitcher’s game: home run to fly ball ratio (HR/FB%).

HR/FB% is fairly straightforward to calculate, as it is the ratio of how many HR a pitcher allows for every fly ball he allows. Whether or not a ball leaves the park is not entirely under the pitcher’s control given the dimensions of each ballpark, the weather conditions, etc. However, pitchers can work to limit the number of fly balls they allow (as I have discussed in my launch angle and exit velocity articles), so this stat is not purely luck-based.

A pitcher's HR/FB% could either be due to luck, underlying metrics/performance, or a combination of both. Diving into the rest of their underlying metrics can give an indication as to whether or not they will maintain their current mark. Let's take a closer look at some pitchers to see whose HR/FB% have been legit and whose have not!

Top HR/FB% Pitchers

All stats current as of Sunday, May 16.

Danny Duffy, Kansas City Royals

(4-3, 1.94 ERA, 1.13 WHIP, 4.0% HR/FB ratio)

Editor's note: This article was written and published before the news of Danny Duffy hitting the IL with an arm injury.

This first player is a veteran who had a promising start to his career, but has not been very exciting over the past several seasons. Danny Duffy now has a career 3.95 ERA, but he has had a fabulous start to this season, compiling a minuscule 1.94 ERA through his first seven starts. Even more impressive is his stingy 4.0% HR/FB ratio (he has allowed just two HR this season), which is fourth lowest among qualified pitchers. Can Duffy continue to pitch at such a high level and avoid giving up long balls?

The first thing I want to look at is his batted-ball profile. Duffy hasn't allowed too much hard contact. His average exit velocity and hard-hit rate are both slightly under league average. However, he has allowed an 18-degree launch angle this season and has consequently allowed the seventh-highest fly ball rate among qualifying pitchers. As I have discussed before, hitting the ball in the air is okay for a pitcher if it is not hit hard. Given how frequently Duffy has allowed fly balls with league-average velocity in a home park that has an average HR park factor, I would not expect to see his HR/FB ratio continue to stay that low.

This is not to say that Duffy will suddenly start to pitch poorly. He has been striking hitters out at a 28.2% clip and has mixed in his secondary pitches well. He has located his off-speed pitches well and has at least a 15.7% swinging-strike rate with each of his slider, changeup, and curve ball. Further, his 3.55 SIERA is a good deal higher than his ERA, but indicates that his batted-ball profile may not be all that incriminating.

So, is Duffy's HR/FB% legit? I would say no based on his batted-ball profile. However, I don't think that means that fantasy managers should look to dump him. I would say that he is a decent sell-high candidate since this is the best start to a season he has ever had, but his strikeouts look to be pretty legit and his batted-profile, while not outstanding, is not bad either.

Kyle Gibson, Texas Rangers

(3-0, 2.28 ERA, 1.04 WHIP, 7.7% HR/FB ratio)

Kyle Gibson has always been a useful fantasy streamer through his career, but this season he has looked like a bona fide rotation option. The 33-year-old has compiled a stellar 2.28 ERA, 1.04 WHIP, and single-digit 7.7% HR/FB ratio over his first eight starts this season. Fantasy managers who roster him have been reaping the benefits, but how long could those benefits last? 

Unlike Duffy, Gibson's batted-ball profile backs up his HR/FB%. His exit velocity and hard-hit rate are both in the top-30 percent of baseball and his 7.8-degree launch angle is encouraging. His 4.04 SIERA and 14.4% career HR/FB ratio indicate that there may be some negative regression coming, but I think signs point more to a legit (or close to it) HR/FB% for Gibson.  

He may not be the most exciting fantasy pitcher, but Gibson has certainly pitched well. He has never been a big strikeout pitcher and his 21.9% strikeout rate is currently higher than his 18.2% career mark, but he has averaged almost six innings per start and has been consistent throughout the season. He offers more in points leagues than in roto leagues, but Gibson appears to be a legit middle to back-end fantasy rotation starter who won't blow up for fantasy managers.

Bottom HR/FB% Pitchers

All stats current as of Sunday, May 16.

Patrick Corbin, Washington Nationals

(2-3, 6.19 ERA, 1.38 WHIP, 27.8% HR/FB ratio)

Patrick Corbin has disappointed fantasy managers this season, posting a poor 6.19 ERA through his first seven starts. Further, his 27.8% HR/FB ratio is the highest among qualified pitchers. He is not the only pitcher who has disappointed so far this season, but fantasy managers are still likely wondering what to do with him. Let's take a look.

Things don't look great upon first glance. Corbin's exit velocity and hard-hit rate are both in the bottom third of baseball, and his 12.6-degree launch angle is a career high. He also has allowed a poor 2.48 HR/9 rate. However, there are some encouraging signs if you dig a bit deeper.

First, Corbin's first two starts, in which he allowed 15 runs, are still dragging his overall numbers down. Corbin has a much-better 3.00 ERA over his last five starts. In terms of his HR/FB%, Corbin has allowed a lot of homers but they have come in uncharacteristic bunches. Corbin has allowed three HR in two of his starts and two in one of them, driving up his HR/FB% and HR/9 rate. While his launch angle is relatively high, his exit velocity and hard-hit rate are not that far off from his career marks. As such, I would expect his HR/FB% to regress towards his career value of a respectable 14.1%.

Corbin's numbers are ugly overall, but he has been trending in the right direction since his first two starts. His batted-ball profile isn't great, but it isn't as bad as his HR/FB% suggests. I think Corbin has experienced some bad luck on long balls and should hopefully continue to see some positive regression as the season progresses. He profiles as a decent buy-low candidate while his overall numbers have not started to reflect his recent performance.

Yusei Kikuchi, Seattle Mariners

(1-2, 4.30 ERA, 1.09 WHIP, 22.6% HR/FB ratio)

Our final pitcher is one who has been mentioned rather frequently this season as a potential breakout candidate. Yusei Kikuchi has not gotten off to the start fantasy managers had banked on, posting a mediocre 4.30 ERA with a 22.6% HR/FB ratio that is just behind Corbin's. Kikuchi has not found success since joining MLB, so is there any reason to believe he can find it now?

There actually are a bunch of signs that Kikuchi may be able to find some success this season. First, while he has allowed a lot of hard contact (his exit velocity and hard-hit rate are both in the bottom quarter of baseball), he has kept the ball on the ground for the most part with a launch angle of 5.3 degrees. His batted-ball profile supports the fact that he has not frequently allowed fly balls. Kikuchi's 26.7% FB rate is actually tied for ninth lowest among qualified pitchers. It could be that Kikuchi just happens to give up HR when he allows fly balls, but his 3.55 SIERA adds to the case that he has more likely been unlucky.

I am hesitant to jump on board and declare Kikuchi a great buy-low candidate simply because he has struggled throughout his career. His 4.30 ERA is actually the lowest of his career, so I don't know I would be fully willing to pull the trigger based on his underlying numbers from a mere seven starts. That being said, the underlying numbers from those seven starts do suggest some bad luck for Kikuchi and hint that he could see better results if he continues to pitch as he has done. Kikuchi does not have the track record that Corbin has, so I would call him a buy-low light candidate. I would prefer to see several more solid starts before I am ready to buy in completely.

More Sabermetrics and Statcast Analysis