clock menu more-arrow no yes mobile

Filed under:

Will the Bullpens Impact the Cubs-Diamondbacks Series?

Close games are expected. A comparison of the bullpens is not one-sided.

Sewald after a save.
Sewald after a save.
Photo by Chris Coduto/Getty Images

The Cubs-Diamondbacks series could impact which team becomes a wild card team. If the season ended on 1 September, the Cubs would be the second NL wild card and the Diamondbacks would be tied with the Giants for the third NL wild card (2 games behind the Cubs). By the end of the season, that could change.

Let’s compare the bullpens of then Cubs and Diamondbacks.

After quickly acknowledging that for the entire season the Cubs bullpen was much better (1.1 WAA vs negative 3.5 WAA), let’s focus on only August. Because bullpens change, that focus will give a better comparison.

Comparison data from Baseball Savant and Baseball Reference.

In August, several statistical measures show that the Cubs bullpen was better:

  • wOBA: .289 vs .346.
  • OBP: .313 vs .342.
  • Home Runs Allowed: 8 vs 18.
  • Hits Allowed (excluding home runs): 60 vs 86.

“Staying on the surface all the time is like going to the circus and staring at the outside of the tent.” — Dave Barry

A Deeper Comparison of Bullpens.

Looking deeper, in August the comparison was not one-sided.

  • The Diamondbacks closer (Paul Sewald) had a higher percentage of got-the-job-done than Adbert Alzolay (82% vs 71%). Got-the-job-done means no earned runs and no inherited runners scored.
  • The Diamondbacks bullpen had 10 saves (7 by Sewald) and the Cubs bullpen had 11 saves (10 by Alzolay and 1 by Mark Leiter Jr.). Although the total saves was not much different, the Diamondbacks seemingly are not as reliant on only one closer, which is an advantage. Extending the comparison slightly past August; on 1 September Sewald and Alzolay each entered their game in the ninth in a save situation. Sewald allowed one single and earned the save. Alzolay allowed a homer followed by two singles for a blown save and a walk-off loss.
  • In August Cubs back-up closer, Mark Leiter Jr., had 1 save in 2 opportunties. On 2 September he blew his next opportunity giving the Cubs a walk-off loss.
  • While Cubs relievers allowed 4 sacrifice flies, Diamondbacks relievers allowed zero sacrifice flies. Advantage Diamondbacks!
  • Each team’s relievers’ total walks and total strikeouts were not much different: Walks: Cubs 45, Diamondbacks 44, Strike-outs: Cubs 99, Diamondbacks 97.
  • The Diamondbacks’ aggressive baserunning can put pressure on the opposing bullpen, especially in close games. In August, 41% of the Cubs’ games were 1-run games, making their bullpen susceptible to pressure from the Diamondbacks’ aggressive baserunning.

“You rely on a different hero every day. That’s what a good team does.” — Torey Lovullo, postgame after win against Orioles on 1 September 2023

The following comparisons excluded relievers with less than 25 PAs and those who pitched in August but were later sent to the minors. Seven relievers from each team remained.

  • The average wOBA and average hits-per-PA of each team’s top three relievers showed the teams closely matched (.249 vs .250 wOBA, .169 vs.166 hits-per-PA). Perhaps that means when a game is must-win, and when the starters each complete 6 innings with equal runs, the teams’ bullpens are equally matched. Perhaps it’s a question of which player steps up to be the hero of the game.
  • Kevin Ginkel had the best wOBA (.217) and OBP (.224) of the remaining relievers.
  • Jose Cuas (Cubs) was the only reliever not to have allowed a home run (50 batters faced). Home runs are relatively less common than other hits but they can make a big impact.
  • Drew Smyly allowed the most homers (7) and the most hits (26).

A Broader Perspective.

Looking at runs allowed and runs scored I’m expecting close games. In August, there was not much difference in allowed runs (128 vs 127), each team with 27 games. Surprisingly the Cubs scored many more runs (149 vs 106). However, that difference in scored runs was largely because of two factors that hopefully will not be repeated in this series:

  • August included the 9-game Diamondback losing streak, during which the Diamondbacks scored 2.2 runs per game. After the losing streak was over, the Diamondbacks averaged 4.8 runs per game for the remainder of the month.
  • August included four games during which the Cubs scored 56 runs (an average of 16 runs per game). Ignoring those four games, the Cubs scored 4.0 runs per game.

If the Diamondbacks keep batting like they have recently, and if the Diamondbacks control the Cubs batters, the Diamondbacks could outscore the Cubs. However, realistically my view is that the games will be handed to the bullpens with the score very close and maybe tied. Because of my expectations of near equality in runs scored and runs allowed, the bullpens’ could make a significant impact on winning games.


The comparison of the bullpens has many perspectives. The comparison is not one-sided. because each bullpen has its’ strengths. Because I’m anticipating close games, whichever bullpen performs better could make a huge difference in the Cubs-Diamondbacks series.

Whichever team wins this series will increase their chances of being a wild card team. Opportunity knocks!