Cubs Relievers Scuffled Against Left-Handed Batters Late in 2024. Is That Problem Now Solved?

You might not have noticed it as you celebrated the holidays, but last week, the Cubs signed Caleb Thielbar to a one-year deal worth $2.75 million. This didn’t generate many headlines, but it addresses something that the team struggled with after the trade deadline.

On Jul. 30, 2024, the Cubs traded Mark Leiter Jr. to the New York Yankees. Just three weeks later, they officially cut ties with Héctor Neris. Though getting rid of both pitchers made sense, the two veteran relievers were first and second on the team in left-handed batters faced out of the bullpen. They were both effective when they faced lefties, too. Left-handed hitters posted a .241 wOBA against Leiter, and a .307 wOBA against Neris. As a reminder, a wOBA of about .320 is considered average.

Sure enough, the bullpen’s performance against lefties struggled without the presence of Leiter and Neris. From the beginning of the season through Jul. 31, lefties posted a .290 wOBA against Cubs relievers, good for eighth in baseball. After that, they had a .333 wOBA, 22nd-best.

Looking at a list of Cubs relievers who faced more than 15 lefties from August onward is not promising, either.
 

Pearson, Hodge, and Miller were good, but those guys were good against almost everyone and are probably bookmarked for higher-leverage usage, rather than exclusively against pockets of lefties. Everyone else was either bad against lefties or (in the cases of Jorge López and Shawn Armstrong) is no longer with the team. 

The Cubs have tried hard to make Luke Little happen, but he needs to show he can find the strike zone often enough before anyone counts on him for much of anything. Even more than that, perhaps, he has to prove he can stay healthy enough to contribute; he missed the entire second half with a shoulder strain. There just isn’t a reliable left-handed pitcher out of the bullpen on this team. That’s where Thielbar comes in, and I am convinced that is why they took a flier on Rob Zastryzny as well. Both of them are, of course, southpaws. Here are both of their career numbers against lefties:
 

Thielbar is the much more reliable of the two, which is why he got a modest but significant guarantee in free agency. He has held his own against righties for his career, as they have a .307 wOBA against him. Zastryzny has allowed a .353 wOBA to righties, and Thielbar’s presence on the roster probably makes Zastryzny's moot. I imagine the Cubs will try to sneak him through waivers as soon as they require a spot on the 40-man roster.

In short, Caleb Thielbar is not the bullpen ace we were all hoping for. Even so, he fortifies a major weakness in the relief corps. He’s a lefty who can reliably get left-handed hitters out. Assuming Jed Hoyer isn’t done adding to this group, this was a really good get.