The Diamondbacks bullpen is better ... and also worse?

The Diamondbacks did many things right in their 74-win 2022 season. The bullpen was not one of them.

This problem is not new. The Diamondbacks have had persistent bullpen issues since the franchise’s inception in 1998.

It is no secret that last year was especially bad, though. In 2022, the D-backs’ bullpen led the National League with 41 bullpen losses and had a combined ERA of 4.58. According to FanGraphs’ wins above replacement metric (fWAR), the D-backs’ bullpen was the worst in the majors last year with minus-0.7 fWAR as a unit. Their bullpen was also the the only one in the league that posted negative WAR for the season.

As would be expected, D-backs relievers also ranked dead last in baseball in win probability added (WPA). That means that, over the course of the season, no team’s bullpen hurt its chances of winning games more than the D-backs’ did.

In 2023, the narrative surrounding the D-backs’ bullpen has flipped. Well, kind of.

Some D-backs relievers have been genuinely fantastic. Andrew Chafin, for example, has yet to allow a run over seven innings. He has also struck out a ridiculous 43.5 percent of the batters he has faced, in large part due to a slider that has the third-highest whiff rate of any pitch in baseball.

highest whiff rate induced on single pitch type, 2023 (min 15 swings):

Félix Bautista splitter: 92.0%
Drey Jameson slider: 73.1%
Andrew Chafin slider: 72.7%
Giovanny Gallegos slider: 69.6%
Gregory Soto slider: 66.7% https://t.co/bg3tkMrJNr

— Sarah Langs (@SlangsOnSports) April 18, 2023

Miguel Castro is also off to a solid start. In 7.1 innings, the 6-foot-7 righty has a 2.45 ERA, 0.95 WHIP and .154 opponent batting average. Drey Jameson was also excellent in the bullpen before making an abrupt transition to the starting rotation last week.

So far this season, D-backs relievers have combined for 0.2 WPA, which means that, as a group, they have had a net positive effect on their team’s chances of winning games. Somehow, at the same time, many of their team bullpen stats are actually worse than they were a year ago.

Wait, what?

As a unit, the D-backs’ bullpen in 2023 has a combined ERA of 4.63, which is up from last year’s 4.58. Their FIP in 2023 is an eye-popping 5.69, much higher than last year’s 4.39. D-backs relievers have also walked 10.9 percent of opposing hitters so far this year, which is the eighth-highest mark in baseball, and also higher than last year’s 9.2 percent.

At the heart of the D-backs’ bullpen struggles in 2023 — and, in particular, at the heart of that ugly 5.69 FIP — is a sky-high home run rate. D-backs relievers have already given up 13 homers in 2023, which is tied with the Detroit Tigers for the most in baseball.

To get a better sense of what’s happening, here is a breakdown of which D-backs relievers have given up those homers:

Player	HR
Scott McGough	3
Drey Jameson	2
Carlos Vargas	2
Cole Sulser	2
Jose Ruiz	2
Kyle Nelson	1
Kevin Ginkel	1

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Many of these homers were allowed by pitchers who have been used mostly or completely in low-leverage situations. For example, Jose Ruiz, who was recently acquired in a trade with the Chicago White Sox, has been used in a mop-up role and figures to continue in that role as long he is with the team. Ruiz’s two homers allowed have come in just two innings pitched.

It is also worth noting that two of the pitchers on the list are no longer on the big-league roster. Namely, Carlos Vargas was sent down to Triple-A Reno last week, and Cole Sulser is now on the 60-day injured list with a strained right shoulder.

Granted, there are a couple of guys listed above who could throw high-leverage innings down the stretch. One of them is Scott McGough, whose return to MLB after pitching in Japan for four years has not been smooth.

Of McGough’s three homers allowed, two came during a save opportunity against the San Diego Padres on April 3. The D-backs lost that one on a walk-off. More recently, McGough allowed a pair of runs to the Miami Marlins on April 15, the latter of which proved to be the difference in a 3-2 loss.

Aside from McGough, D-backs relievers have generally been quite good with the game on the line. At the same time, as a result of poor performances from Ruiz, Vargas, Sulser and others, they have also been horrendous when games were heavily skewed one way or the other.

To illustrate, this table shows a breakdown of D-backs bullpen performance by situation.

Leverage	PA	AVG	OBP	SLG	HR
Low	158	.264	.342	.536	10
Medium	57	.152	.316	.283	1
High	32	.241	.313	.448	2

D-backs relievers — aside from McGough — have generally been good in big moments and very bad in small moments. The result is a bullpen with relatively poor overall stats, but a positive overall impact on winning games.

As for whether or not the D-backs’ bullpen is truly improved in 2023, it is too soon to say. The early returns are promising, though. Most of the team’s most high-leverage relievers have pitched well, and getting 2022 All-Star reliever Joe Mantiply back from the injured list can only help.

Granted, Chafin won’t have a 0.00 ERA for the whole season, nor will Castro’s .211 BABIP hold up for long. But, at the very least, it looks like the D-backs’ bullpen is better — perhaps significantly so — than it was a year ago.

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Top photo: Jeff Curry/USA TODAY Sports