Wednesday, May 29, 2024
AnalysisChicago CubsMLBNational LeagueNL Central

Brad Wieck: The Cubs’s True Southpaw Solution

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Photo Credit: Baseball Savant

For years, the one thing the Cubs could never acquire was something they deeply coveted: a very talented left-handed reliever for the long-haul.

The closest the Cubs got to that pinnacle was with Aroldis Chapman. While probably best-remembered for his triple-digits fastball, his 1.73 SIERA, 1.38 xFIP, 34 xFIP- (average being 100), 45.1 K%, and 35.3 K-BB% in 102 TBF are certainly not something to ignore. In fact, since SIERA was implemented in 2002, Chapman ranks the best out of any single-season SIERA in that time frame for the Cubs. However, Chapman was only around for 3 glorious months and not the long haul.

The Cubs have since tried their luck with specialist types. The best one has been Kyle Ryan and in his time as a Cub, he has posted a 4.28 SIERA, 4.16 xFIP, 94 xFIP-, 22.3 K%, and 11.2 K-BB% in 260 TBF. However, he wasn’t the dominant lefty type the Cubs were looking for. His stats against lefties gave him a fantastic role for the team and against southpaws, he posted a 3.64 xFIP, 23.3 K%, and 14.6 K-BB% in 103 TBF.

However, the solution came to the Cubs on July 31, 2019. The solution came in the form of Brad Wieck.


Acquired from the Padres for right-handed pitcher Carl Edwards, Wieck has impressed throughout his entire minor league career. In that time span, he has posted a 2.91 FIP, 33.2 K%, and 23.6 K-BB% in 1346 TBF.

Perhaps what is most impressive about Wieck’s minor league career was his 2019 stint. While his FIP regressed to 3.88, his K% improved to an astounding 46.4 and his K-BB% reached 37.1 in 97 TBF. While outliers in a small sample, it’s still a very impressive footnote.

To show how dominant those outliers are, when splitting seasons since 2000 using FanGraphs with a minimum of 20 IP, there have been seven pitchers with a K% higher than Wieck’s outlier. Involving his K-BB%, there have been 10 higher. The 20 IP limit is for Wieck’s total IP in his 2019 minors stint, which was 23.1.

Wieck hasn’t slowed down in his major league career either. In his small sample, he has posted a 2.95 SIERA, 3.80 xFIP, 86 xFIP-, 34.3 K%, and 26.7 K-BB%. While his career FIP is 4.33, there’s reason to suggest his HR/FB% could see improvements, as will be mentioned later.

In his 2019 season, he ranked 33rd in SIERA (3.26), 27th in K% (33.1), and 28th in K-BB% (24.3) for relief pitchers with a minimum of 30 IP.


While Wieck is a huge piece for the Cubs next year, that’s not to say he’s without his warnings.

The primary concern with Wieck is how home run happy he was in 2019. His HR/FB% was an alarming 19.5% and his xSLG%, provided by Baseball Savant, was .441. The league average in both stats were 15.3% and .427, respectively. While not egregiously bad, they were absolutely a concern.

However, they may not be all they’re chalked up to be. To start, HR/FB% has 2 predominant flaws: infield fly balls and line drives. The former of which never result in home runs and the latter does. The issue is, HR/FB% takes infield fly balls into account, but not line drives.

To account for this, thanks to the genius of Alex Chamberlain, HR/FB% can be adjusted. To do this, HR/FB% must be adjusted to be calculated as HR/(oFB+LD)%. While line drives can be found on FanGraphs, outfield fly balls have to be manually calculated with the following equation: FB * (1-IFFB%). Given this, we find Wieck’s, in 2019, to be 14.8% and, for his major league career, 14.2%. The league average HR/(oFB+LD)% in 2018 was 8.4% and, in 2019, was 10.2%. While still below league average, it’s definitely an improvement over his previous.

When looking at Wieck’s HR/(oFB+LD)% in Chicago, the number drastically drops to 9.1%. When getting a bit crazier and combining that sample with his 2018, to combine for a 274 pitch sample, the number becomes 10.0%. So, despite playing with small samples throughout this entire process, not everything is as bad as it seems.

Another thing to watch for Wieck is if he overperformed his xSLG% in San Diego. Last season, in a sample of 181 pitches, his xSLG% in Chicago was 210 points lower than his for the whole season, at .231. In 2018, with 93 pitches, his xSLG% was 93. The downside is how high his xSLG% was with San Diego. In a sample of 452 pitches, Wieck had an xSLG% of .509. It’s important to note, however, small samples are being dealt with no matter what with Wieck.

Wieck’s xwOBA, from Baseball Savant, plays a very interesting role in this as well. In his 2019 season, his xwOBA was .318, which ranked just 0.1 under the league average. However, his xwOBA and Hard Hit% have an intriguing relationship, with the latter provided by Baseball Savant. To illustrate this is the chart below.Wieck's Hard Hit% vs xwOBA by Month-2.png

The primary thing this graph illustrates is the uncertainty of dealing with his small sample size. As seen, some months can have a low Hard Hit% and high xwOBA (April 2019) and some can see an increase in Hard Hit% but a decrease in xwOBA (May to June 2019). The r2 also illustrates that well. The r2 of Hard Hit%’s trendline sits at 0.122 and, for xwOBA, 0.004. So, while it’s generally logical to assume that Hard Hit% and xwOBA have a direct, upwards correlation, Wieck’s data hasn’t shown enough of a trend to fully conclude this. However, given his aforementioned peripherals and xSLG% trend, it’s logical to conclude that his xwOBA could see improvements with a larger sample size.


Given his stats compared to other Cubs, Wieck’s best role is in a set-up situation. While Brandon Morrow and Dan Winkler, the current Cubs’s set-up, have the pedigree that Wieck lacks in a larger sample, they also have had their fair share of concerns. The concerns preeminently involve their health.

Wieck certainly has the stats to be a set-up man too. The best SIERA in the Cubs’s bullpen last year with a minimum of 30 IP as a Cub, was Brandon Kintzler at 3.81. The leader in K% and K-BB% was Strop, at 27.5 and 16.3 respectively. Wieck, despite splitting seasons, pitched 34.2 innings in 2019 and posted better numbers in all 3 stats.


For the Cubs, Wieck is the perfect relief pitcher, he is someone that they can mold into a very valuable talent in many roles. As aforementioned, his amazing statistics strongly imply that he can fill in any roll well. Next year will be the first time Wieck gets his chance, and his statistical pedigree suggests that it will go very well.

All stats are from FanGraphs unless otherwise noted.

Steven Pappas

Hello! My name is Steven Pappas, and I'm a high school junior. I love to analyze and write about baseball data as a huge Chicago Cubs fan and lifelong follower of the sport. I use large databases such as Baseball Savant, basic coding knowledge in RStudio, and my inquisitive mindset to always scour the infinite data available. I really enjoy watching and following basketball and am a Chicago Bulls fan, actively going to their games at the United Center. I love the study of filmmaking, and it's a passion that I've begun to explore as a career opportunity. My favorite works come from the minds of Stanley Kubrick, Yorgos Lanthimos, Alejandro G. Iñárritu, the Coen brothers, and Wes Anderson. As a deft and passionate writer, I use my proficiency to create works from baseball data, for films, and my ideas in the form of short stories and little nuggets. I'm also a libertarian socialist in training and an active Greek Orthodox Christian.