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Evaluating Pitchers With New Homes Using HRPF+

After I developed directional home run park factors and converted them to a plus metric, I covered hitters who have a new home in 2020. For this portion of the series, I’ll cover some of the top starting pitchers with new clubs. Of course, there are outside factors like switching leagues and facing unfamiliar opponents but I have tried to include that in my analysis. In case you’re new to my work, I’ll cover the directional park factors real quick. For the full explanation, you can check out the original article here and the conversion to a plus metric, here.

Guts of Directional HRPF+ 

I pulled three years of batted ball data from all 30 MLB venues. Then, I broke down the data by direction: left, center, right. From there, I separated the barreled balls that were hit to each field and how many of those barrels turned into home runs. That’s the home run per barrel rate (HR/BRL%) to each field. I refer to this metric a lot, especially in my eHR metric. Of course, I found out that HR/BRL% was much higher for pulled balls than for balls hit to the opposite field. So, I had to separate all data for right-handed and left-handed batted balls. then, I ran Z-Scores using all this data for each venue to determine how left, center, and right fields compared to the league average. That’s the genesis of the data.


However, nearly 20% of all home runs were hit with a quality of contact below that of a barrel. Jonathan Metzellar of PitcherList explains this very nicely in his most recent article, Beyond the Barrel. Most of the remaining home runs are qualified as Solid Contact. Balls that qualify as solid contact are home runs between 10 and 11% of the time. I certainly had to account for those, so I devised a formula to include them in the park factors. I won’t bore you with more details and data, so let’s get to the pitchers!

I won’t cover Corey Kluber or Jordan Lyles because Globe Life Park is no more in 2020. The Rangers will have a new home with a retractable roof and a more controlled environment and different dimensions. So, the data for Globe Life Park is unfortunately useless. 

The park factors that I reference (HRPF+) measure how much better or worse a park plays for home runs based on a percentage. 100 is league average in terms of home runs relative to the same direction. For every point above or below 100, the park is 1% better or worse than league-average.  In other words, if a park is valued with a HRPF+ of 110 to left field, it’s 10% better to left field for home runs than the league average left field. The same goes for HRPF+ below 100.

Madison Bumgarner (SP – ARI) from SFG

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Oracle Park (SFG) 89 65 57
Chase Field (ARI) 106 68 98

While we only have two years of data from Chase Field since the humidor was installed, it’s clear that Mad Bum gets a downgrade to right field. Why? Because, well, right field at Oracle Park is 43% below the league average and ranked 30th for home runs hit. That was a good thing for him when he pitched there but now that he’s gone, he won’t have that advantage. Left-handed batters managed a 48.7% HR/BRL rate over the last three years at Oracle. For reference, the league average HR/BRL% for left-handed batters to right field is 75.8%. Centerfield was equally helpful for Mad Bum but what about left field? Bad news for Mad Bum. Since 2015, here are the HR/FB% to left field for Bumgarner in succession 16.4%, 23.8%, 24.2%, 30.6%. That’s a disturbing trend in a home park that played 11% below league average to left field. Now,  he calls Chase Field home that’s played six percent better than league-average to left field. Last year, Bumgarner ended up with a career-worst 12.6% HR/FB rate, which considering the juiced ball, wasn’t half bad. I can say with quite a bit of confidence, that Bumgarner sets a new career-high in home run rate, settling in with an ERA above 4.00.



Zack Wheeler (SP – PHI) from NYM

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Citi Field (NYM) 110 107 105
Citizens Bank (PHI) 115 91 114

Well, this isn’t quite the park downgrade most skeptics are projecting. To be fair, Citizens Bank Park does play more favorably for hits in general and therefore runs scored, so it is a better hitters park overall. However, for home runs, it’s very close. Outside of 2017, Wheeler has always been able to suppress home runs. And, since both left field and right field are within 10% in terms of my HRPF+, let’s focus on centerfield. Citi Field is seven percent worse than league-average (for a pitcher) on home runs to center where Citizens Bank is nine percent better than league-average to centerfield. Over the last three seasons, one-third of Wheeler’s fly balls traveled out towards centerfield. In 2017, something weird happened. Wheeler gave up an astonishing seven of his 15 home runs to centerfield in just 86 innings. Since then, he’s allowed just five homers over the last two seasons combined. His HR/FB% to centerfield over that timeframe is just four percent, which is lower than half of the league-average. Based on the scant number of homers he’s given up to center, I don’t think I can regress that number anymore. In other words, this move is essentially neutral with maybe a slight downgrade overall for Wheeler.

Hyun-Jin Ryu (SP – TOR) from LAD

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Dodger Stadium (LAD) 98 150 95
Rogers Centre (TOR) 110 101 102

In 2019, we saw everything come together for Ryu, health, home run suppression, weak contact, luck, etc. It was a best-case scenario type of season. Now, he finds himself in the AL East. Without knowing anything about park factors, we can safely assume the competition will be more difficult. Not only is the division better, but he’ll face an extra hitter in the DH instead of the pitcher twice. However, he will receive a much more giving centerfield compared to LAD, but he’s only given up eight home runs to centerfield the last two seasons. So, maybe he gives up three this year? How about left field? Ryu’s given up 47 home runs since the start of 2017, 24 of them have gone out to left field (51%). Left field at the Rogers Centre is 12% more favorable for home runs than Dodger Stadium. Ryu’s HR/9 last year was just 0.84. For 2020, I’ll set the over/under at 1.20. Given neutral luck, I’d expect something close to an ERA of 4.00. That’s not all that playable with a below-average strikeout rate.



David Price (SP – LAD) from BOS

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Fenway Park (BOS) 96 68 75
Dodger Sta (LAD) 98 150 95

Price is in for a massive spike in home runs to center and right fields. Throughout four seasons with Boston, his HR/FB% to right field hovered around 10%. To centerfield, it was slightly lower with a HR/FB% around 9% but spiked in 2019 to a career-high 12.8%. I think it’s important to note that during his time with Boston, he gave up 33 home runs at home and 45 home runs on the road. He did throw 21 more innings on the road over that time but doesn’t account for a difference of 12 homers. I decided to look at wOBA minus xwOBA on all fly balls and line drives against Price since 2015 on batted balls to center and right field. It’s essentially wOBACON minus xwOBACON to CF and RF but excluding ground balls. 

Season LD+FB: wOBA-xwOBA (CF) LD+FB: wOBA-xwOBA (RF)
2016 -.021 -.007
2017 -.051 -.039
2018 -.124 -.044
2019 -.180 -.166

I trust Statcast’s data more in 2018 and 2019 as the kinks have been ironed out. That’s where the biggest discrepancy lies between wOBA-xwOBA. A portion of the difference can be attributed to the stellar outfield defense between Mookie Betts and JBJ. Fortunately, Betts will be roaming right field once again, so that’s a wash. Bellinger in center is a slight downgrade from Jackie Bradley Jr. But, overall, I think Price continues to partially outperform his expected metrics on balls hit to center and right on balls that stay in the yard. However, given the increase in home runs he may allow, the gap between LD+FB wOBA-xwOBA should be much smaller. That being said, the smaller outfield dimensions from left-center to right-center at Dodger Stadium should turn some doubles and triples into outs. It’s difficult to predict how this will play out. On one hand, he’ll turn doubles and triples into outs. On the other hand, the doubles/triples that he would have allowed in Fenway may turn into home runs. His ERA may go up due to the homers but I expect his WHIP and strikeouts to improve as he avoids the DH and will face weaker opponents.

Kenta Maeda (SP – MIN) from LAD

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Dodger Stadium (LAD) 98 150 95
Target Field (MIN) 97 82 94

Okay, his one is easy. A negligible change to both left and right fields, but look at centerfield! Dodger Stadium is an incredible 68 percent more favorable for home runs to centerfield than Maeda’s new home, Target Field. Over the course of his career, Maeda has given up more fly balls to centerfield than to left or right fields, respectively at nearly 40%. He definitely felt the juiced ball with a HR/9 of 1.47 in 2017 and 1.29 in 2019. However, in 2018, he allowed just a 0.93 HR/9. It seems like the generous centerfield at Dodger Stadium played a role. His 15.8% HR/FB to centerfield last year was the worst of his career and about 5% worse than the league-average. Yet, he allowed fewer home runs per fly ball than the league-average overall. This proves that Dodger Stadium hurt his number, and he allowed 13 of his 21 home runs at home in 2019. The move from the NL to the AL isn’t ideal but the AL Central has its weaknesses. Detroit and Kansas City are poor clubs and have favorable parks to pitch in. Cleveland is top-heavy but not all that deep and the White Sox are talented but young. I would bet that Maeda knocks a few home runs off his total in 2020 and ends with a sub-4.00 ERA for the second time in four years. I want Maeda over Ryu this season and it’s not all that close.



Dallas Keuchel (SP – CHW) from ATL

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
SunTrust Stadium (ATL) 88 100 100
U.S. Cellular (CHW) 110 107 113

Keuchel had a wild 23.1% HR/FB rate last year with the Braves in an abbreviated season. Normally, a ratio that high would be a death sentence to a pitcher’s ERA. But, Keuchel still managed an ERA of 3.75 thanks in large part to a 60% ground ball rate. His sinker and changeup both generate a ton of ground balls. However, his sinker was crushed when elevated in the strike zone. On his sinker, he gave up six home runs on just 16 fly balls in 2019. Moving from Atlanta to Chicago is clearly a negative for Keuchel, not only because the park is more favorable for hitters to all three fields but he’ll also face the DH. Because Keuchel gives up so few fly balls, I don’t think it’ll completely decimate his ratios given the park change. I’m more concerned about his dipping zone rate. It hit a career-low 33% last year and hitters aren’t exactly chasing often enough to justify the drop. It showed up in his walk rate that went from 6.6% in 2018 to 8.0% in 2019. His strikeout rate will once again be below 20% and if his walk rate jumps to nine or 10%, he could finish with a 4.50 ERA in 2020.  

Wade Miley (SP – CIN) from HOU

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Minute Maid (HOU) 136 73 129
GABP (CIN) 121 132 136

Miley jumps from one hitter’s haven park to another. At least he leaves the American League and the DH to go to the NL where lineups are generally weaker. Great American Ballpark is the most favorable (or unfavorable for pitchers) for home runs in all of baseball. Minute Maid Park in Houston is a hitter’s park to both left and right fields, so there’s a minimal change for Miley on pulled and opposite-field fly balls this coming season. Then, there’s centerfield. If you recall, Minute Maid used to have Tal’s Hill in center field and was 435 feet to dead center. In 2015, the hill was removed and the fences were brought in to a distance of 409 feet to dead center. My park factors only include the results after the fences were brought in and it still performs poorly to centerfield. That’s because the left-center field fence is 404 feet away from home plate. Okay, enough about Houston, let’s focus on Miley. He gives up a lot of fly balls to centerfield. In fact, over 40% of his fly balls head out to center. He gave up just three homers to center last year with just a 4.9% HR/FB rate. I expect that to at least double if not triple in 2020. That could be the difference between three and nine home runs to centerfield over the course of a full season. With an unknown opening day, I think he may give up three or four more home runs in 2020 then if he stayed put in Houston. 

Cole Hamels (SP – ATL) from CHC

Park (Team) LF HRPF+ CF HRPF+ RF HRF+
Wrigley Field (CHC) 105 106 79
SunTrust Stadium (ATL) 88 100 100

Entering the twilight of his successful career, let’s find out if Hamels can bring back some fantasy goodness in the ATL. While Wrigley has a higher HRPF+ to center field, it’s mostly due to the cheap home runs when the wind is blowing out. The difference between the two parks and their three-year average in terms of HR/BRL% is within one percent. Hamels will see more significant changes to left and right fields. As a left-handed pitcher, he sees the righty-heavy lineups most of the time. Righties have done pretty well against the southpaw with a .330 and .321 wOBA in 2018 and 2019, respectively. The good news for Hamles is that 60% of the home runs he’s allowed since the start of 2018 have gone to left field. Wrigley was slightly favorable for home runs to left where SunTrust should suppress them a bit more. I expect Hamels to allow fewer home runs to left field in his new park but the short porch near the right-field line could allow for some non-barreled balls to drop just over the fence. I’m not chasing Hamels in drafts even though he’s cheap. I’d look for upside plays such as Corbin Burnes, Justus Sheffield, and Kwan-Hyun Kim over the crafty veteran. 

Follow me @FreezeStats. Check out my work at FantasyPros and Pitcher List.





Photo courtesy AP Photo/John Bazemore