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Brian Duensing: The unsung hero of the Cubs’ bullpen

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A closer look at the lefthander’s outstanding 2017 season.

Brian Duensing pitching against the Brewers at Miller Park
Photo by Stacy Revere/Getty Images

There weren’t a lot of blockbuster moves in the Cubs’ off season. In retrospect, the most important move was turning Jorge Soler into Wade Davis (who has saved 31 games in a row, besting the old franchise record). While it’s easy to celebrate that move now, it’s worth remembering that even that move wasn’t a sure thing. Davis spent last year dealing with forearm issues that left a lot of people wondering if he still was an elite closer.

Most of the moves the Cubs made were stopgap moves to replace players they lost to free agency. Dexter Fowler took a big payday in St. Louis so the Cubs signed Jon Jay. Jason Hammel didn’t want to risk moving the bullpen so the Cub acquired Eddie Butler and Brett Anderson hoping one of them would become a fifth starter. Travis Wood and Trevor Cahill wanted the opportunity to start, and in a move that very few people paid much attention to in early December the Cubs signed middle reliever Brian Duensing to a one year contract in the hopes that he’d be able to eat some innings and keep the Cubs competitive. Some of these deals were more successful than others but with quiet consistency Duensing is proving to be a crucial acquisition as the Cubs try to stave off the Brewers in the final few weeks of the regular season.

The Cubs bullpen might be the most exclusive dance club in Wrigleyville, but let’s be honest: middle relief isn’t baseball’s sexiest job. In looking at the bullpen’s ERA, FIP and K/9 by month we can see some inconsistencies in the bullpen. While most of us are familiar with Earned Run Average (ERA) a reminder that Fielding Independent Pitching (FIP) is the ERA we should expect based solely on elements the pitcher can control and K/9 is the number of strike outs averaged over 9 innings. I mean, this table pretty much tells us what we’ve all see in the late innings this year.

Cubs monthly bullpen splits

Month ERA FIP K/9
Month ERA FIP K/9
Mar/Apr 2.87 3.71 10.23
May 3.49 4.36 9.47
June 3.55 3.43 10.56
July 3.36 4.03 9.35
Aug 4.96 5.59 8.93
Sep 6.05 3.47 10.64
ERA, FIP & K/9 by month - 2017 Fangraphs

With the exception of Davis, nearly every arm in the pen has struggled at some point in time. Carl Edwards Jr. inexplicably lost his curve ball after the All-Star break (thankfully, he seems to have found it again). Pedro Strop occasionally loses the plate for long stretches of time. Hector Rondon and Koji Uehara have both spent time on the disabled list (and are currently day-to-day) after some outings where they seem to have been throwing batting practice. Justin Grimm… well, let’s just say there is a reason that Grimm has been riding the shuttle back and forth to Iowa all season.

However, quietly, in the fifth, sixth or seventh inning, there has been Brian Duensing. With a 2.47 ERA, 3.26 FIP and 8.95 K/9 Duensing is having the best major league season of his career. For comparison, in his last year with a similar workload (2015 with the Twins) Duensing had a 4.25 ERA, 5.02 FIP and 4.44 K/9. That is a dramatic difference as we can see in the below charts:

Brian Duensing ERA by year
Fangraphs
Brian Duensing FIP by year
Fangraphs
Brian Duensing K/9 by year
Fangraphs

It’s worth taking a closer look at how Duensing’s managed to position himself as one of Joe Maddon’s most reliable middle relief arms. Unlike many relievers, Duensing has four pitches. According to Fangraphs, in 2017 he’s thrown his fastball about 49 percent of the time, a slider about 24 percent of the time, and splits the rest of his pitches between a curveball and a change-up. That is a change from previous years. Over his career Duensing threw his fastball 58 percent of the time, his slider 21 percent of the time, his change-up 13 percent of the time and only threw his curveball eight percent of the time. The result is that even though his fly ball percentage (FB%) is up, his line drive percentage (LD%) and home run to fly ball ratio (HR/FB) are down.

So many numbers, Sara, what does all of that mean? The bottom line is that Duensing is changing his speeds and location more and while it’s resulting in more fly balls, thankfully they aren’t being hit as hard. This has allowed Duensing to be one of the few pitchers who isn’t getting pounded for home runs at a time where other pitchers seem to be having the opposite problem.

There are reasons to be cautious that Duensing will continue to perform at this level. For starters, it’s not in line with anything he’s done in his major league career — he’s having the best stretch of his life and baseball statistics tend to normalize. Additionally, even though his second half ERA is a minuscule 1.83 and an improvement over the 2.79 ERA he put up in the first half, his FIP has been an identical 3.26 in both. In other words, he’s getting a bit lucky and over performing his peripherals since the All-Star break.

Perhaps the most concerning element of Duensing’s second half is that his K/9 number appears to be coming back to earth. In the first half that number was 10.94, so far in the second half it’s 5.03 (which, incidentally, is much more in line with his career average). He’s just not striking out people as much in the second half and there is a risk people will eventually start hitting him harder.

If the Cubs are going to win the division and make a run in the post-season, it’s pretty clear that they need Duensing’s career year to stretch out at least a tiny bit longer. The Cubs are clinging to a 3.5 game lead over the Brewers with 12 games to go, it’s imperative that they stabilize the bullpen as much as possible. Duensing maintaining these numbers for another month and a half is as critical of a component of Cubs’ bullpen success as Mike Montgomery resuming his role as the long reliever.

And who knows? If these numbers hold up and he’s willing to sign on for another year at $2 million, I think the Cubs should take a chance on one of their most reliable arms of 2017.