Cubs bullpen has impressed – but there’s a long ways to go

Going into the season there were considerable questions around the Chicago Cubs bullpen, but they’ve impressed in the early going. In the first game of this week’s two-game series against the Fighting LaRussas, the Chicago Cubs had a true bullpen game on a cold, windy, wet early April -er – May evening, during which five Cubs relievers surrendered a total of just one earned run.

Keegan Thompson was the bulk guy, going 3 2/3 innings and surrendering just that earnie on a solo homer. The Cubs trailed most of the game, so the other four pitchers were mostly B-side relievers: Scott Effross, Michael Rucker, Mychal Givens, and Chris Martin.  Those last three combined for four innings of shutout baseball.

Yes, the conditions were reminiscent of a rainy Scottish moor (45 degrees Fahrenheit,* soggy turf, and a gentle 23 MPH breeze at game time), and the White Sox were missing some of their big bats, but you play the opponent and weather you’re dealt. This was an encouraging performance from relievers who, if things had been going to plan, would not have been given this much responsibility at this point in the season.

*That would be 7 degrees Celsius in Scotland

The result wasn’t just because MLB has decided to use repurposed potatoes as game balls. Even compared to other bullpens, the Cubs relievers stand out. They rank second or third in the majors in all the following stats: K percent, K-BB ratio, xFIP and SIERA. How do you think they do it? What makes them so good?

The relievers’ pitch selection gives one clue. The Cubs relievers have thrown curves and cutters at a higher rate than any other team (first in curves, third in cutters). David Robertson leads the way here: those are the only two pitches he’s thrown in anger in 2022. (Well, according to Fangraphs Pitch Info data, anyway – other sources show him using a slider. The discrepancy seems to center on the degree to which some of his harder curves are classified as sliders.) Rucker, Thompson and Rowan Wick (who did not appear in the first White Sox game) all throw cutters and curves at or near double-digit frequencies (Rucker’s cutter percent is 9.7).

Cubs: The relievers are succeeding with fewer sliders

The flip side involves the pitch types Cubs relievers don’t throw as often as the league average: fastballs and sliders. The Cubs relievers rank 18th in four-seamer usage, 18th in slider usage, and 21st in sinker usage. Most teams have moved away from the sinker in recent years, but the Cubs aversion the slider is unusual.

Much of this can be written off as nano-sized sample data, but the Cubs have been avoiding sliders for a while. You have to go back to 2015 to find a North Side relief corps in the top half of the league in slider usage. This seems to be more the result of long-term roster construction priorities than random small-sample matchups.

Perhaps the Cubs have found a market imperfection here. The slider is in high demand; it might have priced itself beyond what the Cubs front office thinks is reasonable. Curves provide good results too, arguably at a lower cost per pitch. This might be one way to assemble a cost-effective bullpen.

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This is all speculation, of course. If usable price-per-pitch data exists, I haven’t seen it. But the Cubs’ consistent attempt to field a good bullpen without relying on the slider is an interesting under-the-radar story to follow as the season progresses. David Ross certainly hopes this bullpen can continue to suppress runs as well as it has thus far. He probably hopes even more fervently for the return of Wade Miley, Adbert Alzolay, and the 2020 edition of Kyle Hendricks.