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Statcast Pitcher Studs and Duds - wOBA-xwOBA Difference for Week 10

Welcome back to RotoBaller’s pitchers Statcast studs and duds article series! Each week we will select an advanced stat, choose two studs and two duds, and analyze what those stats could mean for future fantasy output.

My first article in this series involved expected weighted on-base average (xwOBA) against and I hinted that we could eventually compare pitchers’ actual wOBA to their xwOBA once we had more data to identify relative underachievers and overachiever. Well, that time has come! You can check out that first article here, where I describe the actual metrics.

This exercise will be particularly helpful for fantasy players because pitchers should perform towards their expected metrics over the course of the season. Identifying players who are outperforming or underperforming their expected metrics can help us pinpoint potential buy-low and sell-high candidates beforehand. With that goal in mind, let’s take a look at some wOBA-xwOBA differences!

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wOBA - xwOBA Difference Studs

For reference, the league-average wOBA against is .323 and the xwOBA is .323 (difference of 0). All stats current as of Monday, June 2, courtesy of


Eduardo Rodriguez - Boston Red Sox

wOBA: .328, xwOBA: .303, Difference: .025

Our first wOBA-xwOBA stud is one who has teased us with fantasy talent in the past but has not yet been able to put it all together. Eduardo Rodriguez has shown that he can post high strikeout numbers but has also shown a lack of command and a propensity for getting injured. His 5.04 ERA and 1.40 WHIP through his first 60 2/3 innings pitched this season are certainly not encouraging. However, the difference between his xOBA and expected wOBA suggest that he has been unlucky and should have a solid wOBA compared to the rest of the league. Could Rodriguez be the buy-low candidate that could help you in a big way down the road?

Rodriguez has a lot going on under the hood that suggests he should be performing better than he has been. First, he has done a great job at limiting hard contact (86.6-MPH average exit velocity, 29.7% hard-hit rate, 11-degree launch angle) yet has gotten unlucky on balls in play. Rodriguez has a bloated BABIP (.345 compared to a .298 career mark) and a 1.40 WHIP despite having a respectable 7.6% walk rate. Further, his 4.02 SIERA, while not great, is over a run lower than his ERA, suggesting that he has pitched better than his peripherals reflect.

Additionally, Rodriguez has still displayed the main attribute that fantasy players have always liked about him, his strikeout potential. E-Rod has a 25% K rate to this point and has at least a 10% swinging-strike rate on four of his five pitches, the highest being on his devastating changeup. There is a lot of promise behind his poor numbers and I would definitely try to buy low on him before things start to pan out.


Dylan Bundy - Baltimore Orioles

wOBA: .335, xwOBA: .313, Difference: 0.22

Our second wOBA-xwOBA stud has had a similar fantasy story in many ways to E-Rod but has been even more frustrating. Bundy has managed to stay relatively healthy across his career but has been crippled by the long ball. His 4.58 ERA and 1.98 HR/9 over his first 59 IP seem to indicate that things have not changed. However, his .313 xwOBA is well below the league average. Is there some hope that Bundy can still provide fantasy value?

Bundy’s fantasy value can really be boiled down to whether or not he can keep the ball in the yard. His WHIP (1.24), walk rate (8.4%),  and K rate (23.9%) are all good enough, so his batted-ball profile becomes all the more important. Things in this department are a mixed bag. Bundy has allowed 13 HR this season but has done a good job of limiting hard contact (31.3% hard-hit rate, 88 MPH exit velocity). His 16.1-degree launch angle leaves something to be desired, but launch angle alone, especially combined with his solid contact numbers, does not dictate home runs.

Overall, Bundy’s numbers, while not entirely discouraging, do not present enough support for me to buy into him fully. His batted-ball profile overall is pretty good, yet he has still continued to give up HR. His xwOBA suggests future improvement, but his 4.37 SIERA is in line with his ERA. I would be willing to go after him in a deep league, but he needs to show improvement in his peripherals before I would consider him in a 12-team league.


wOBA - xwOBA Difference Duds

For reference, the league-average wOBA against is .323 and the xwOBA is .323 (difference of 0). All stats current as of Monday, June 2, courtesy of


Shane Bieber - Cleveland Indians

wOBA: .300, xwOBA: .347, Difference: -.047

Our first wOBA-xwOBA dud has been very impressive this season across the board. 24-year-old Shane Bieber is in just his second big-league season but has a stellar 3.11 ERA, 1.05 WHIP, and 30.3% K rate in 63 2/3 inning pitched. That being said, the .047 difference between his xOBA and xwOBA suggest that there may be some lacking aspects of his game. Is Bieber a legit high-end fantasy starter for the rest of the season?

Bieber has some conflicting signs in terms of his overall performance. Firstly, his pitch arsenal in itself isn't impressive; his fastball sits at 93.2 MPH and his slider and curveball don't have a ton on spin on them. Despite this, he has managed a strong 30.3% strikeout rate.

Further, Bieber has managed to keep his ERA and WHIP down despite a poor batted-ball profile. He has gotten hit quite hard this season (90.9-MPH exit velocity, 46.9% hard-hit rate, 14.4-degree launch angle) yet has not seen the negative effects to this point. His 3.37 SIERA suggests that there is nothing to worry about, but his .274 BABIP is much lower than his .356 mark last season.

Bieber is a tough case to crack for me. He has had great success despite having mediocre stuff and getting hit hard. His performance is only partially supported by his underlying metrics, and some of his metrics are pretty damning. Bieber is, of course, a great dynasty asset given his young age, but I cannot fully buy into him at this time. There are too many signs, including the difference between his actual and expected wOBA, that give me pause.


Jake Arrieta - Philadelphia Phillies

wOBA: .327 , xwOBA: .344 , Difference: -.017

This pitcher used to be a flamethrower and a major fantasy asset but has posted a pedestrian 3.96 ERA with an xwOBA that is higher than his current wOBA and the league-average xwOBA. Jake Arrieta had a lackluster first season with the Phillies in 2018, and things have continued to trend in that direction, more or less. Will he be able to help fantasy owners for the rest of the season?

The 33-year-old has definitely made some changes in terms of his pitching style over the past several seasons. Arrieta has ditched the straight fastball in favor of a sinker exclusively, his main fastball pitch. He has also switched up his main arsenal to a duo of sinker and changeup (a classic strategy to keep hitters off balance) over the power slider. Arrieta is now pitching to contact (82.2% contact rate) over power pitching. He has gotten hit relatively hard (89.3-MPH average exit velocity, 38.8% hard-hit rate) but he has kept the ball the ball down in the zone and balls in play on the ground (7.4-degree average launch angle).

Arrieta has been pitching more carefully but effectively. As a result, his WHIP (1.36) has gone up, mostly due to an increase in walks (8.5% walk rate). This is likely the cause of Arrieta’s xwOBA being higher than his actual wOBA. Therefore, I wouldn’t necessarily be concerned with the difference in his actual and expected metric. Further, his .297 BABIP is a good deal higher than his career .272 mark, indicating further that he has been getting unlucky on balls in play. Finally, Arrieta’s 4.59 SIERA is much higher than his ERA, but as I have mentioned before, I think he has done an overall good job in terms of his batted-ball profile, so I am not really worried.

Arrieta’s change in pitching style has negatively affected his xwOBA, but I don’t think that his xwOBA indicates that he will not continue to be a decent middle-of-rotation to back-end fantasy starter. The rest of his stats point to him being able to provide fantasy value as a contact pitcher, less value than in the past when he was more dominant, but value none-the-less. His numbers aren’t strong enough to sell him at this time, but fantasy owners should not be worried about dropping him either.


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