The implosion of the Arizona Diamondbacks bullpen

That was then, this is now

Let's start off with a look at the bare bones. Here are the stats for our relief corps up to and since the All-Star break.

The difference is obvious. An ERA fractionally short of two and a quarter-runs higher than in the first half. Ironically, the team actually has a winning record, but that's largely due to games like last night, where the bullpen blew a lead and the offense then bailed them out. The last time our relievers "won" a game where there wasn't a blown save involved, was August 7, when Daniel Hudson vultured a W for getting the last out of the fifth inning in a 9-3 win over the Brewers. I'd say the last "real" win was earlier that series on the 5th, when they worked five scoreless frames, and the D-backs won 3-2 in 11 innings.

Interestingly, the bullpen is striking out somewhat more people than they were in the first half. However, that isn't enough to counteract a greater rise in walk rate, from 3.9 to 5.3 BB per 9IP, and a huge spike in home-run rate, which has increased massively, from 0.96 to 1.79 HR per 9IP. This becomes particularly obvious if you break the bullpen stats down to individual months. Over the first month of the season, Arizona's relievers only allowed five home-runs in 103.1 innings of work. But over the last full month, July, even though they threw 25 fewer innings (in part due to the All-Star break), they allow a startling 18 home-runs. Here are all the monthly figures.

What this shows is that this hasn't been a sudden switch in performance at the All-Star game, but a steady decay. The Diamondbacks' bullpen ERA has increased each full month of the season - the final week will decide whether that happens again in August. Even though the strikeout rate was at its best in July, that was not nearly enough to counter the horrendous frequency with which pitches were leaving the park. This month, the home-run rate has regressed somewhat, but the K:BB ratio has dropped to a season low, little more than three strikeouts for every two walks (76:48).

I also note there does not appear to be a direct correlation between use and performance. The bullpen was certainly sorely taxed in the first month, averaging virtually four innings a game. But they responded with the only sub-four ERA of the year so far. Now, there is a possible case for delayed effect here: the innings logged there are now coming home to roost in tired arms during the second half of the season. But overall, in the second-half, the Diamondbacks have thrown fewer relief innings than the Marlins' and Brewers' bullpens, whose post-break ERAs added together would still be less than Arizona's over that time.

Ch-ch-ch-changes (in personnel)

The bullpen now is a very different creature from what it was on Opening Day, with Jake Barrett, Randall Delgado and Daniel Hudson the only survivors. Veterans Tyler Clippard, Josh Collmenter and Brad Ziegler have all left the building. How much of an impact has that had on the team? Some - though not as much as you'd think. Discounting the innings thrown by Clippard, Collmenter and Ziegler, while the first half ERA increases, it's only about a quarter-run higher, at 4.75. The figure for the second half, again dropping the same three players, is still more than two runs worse, at 6.84. So it's not just the loss of experience.

To try and figure out what else had gone wrong, here are the stats for everyone to have pitched out of the bullpen in the first and second half. Note that the figures for Rubby De La Rosa (1st half), Patrick Corbin (2nd half) and Zack Godley (both halves) reflect their performance as both starters and relievers, since we're trying to establish an overall level of performance change.

You can see that the struggles have afflicted many members of the pen: Jake Barrett and Daniel Hudson are the two most obvious examples, and these were the two men expected to step up after the departure of Clippard and Ziegler. Additionally, we've seen the regular use of Dominic Leone. He is less than a handful of innings away from our most used reliever in the second half. Meanwhile, as Steven noted last night on Twitter, Leone is cementing his position as the worst reliever in Diamondbacks' franchise history, with an ERA more than a run above anyone else to have thrown 20+ innings out of our bullpen. When he's coming in for any high-leverage situation, as yesterday - there are problems.

I think the causes of the issue is a combination of factors. We have the loss of the reliable arms, in Ziegler, Clippard, etc. The inability of Hudson, Barrett to sustain their solid first-half performances. And then there's the lack of depth: those who have been new additions to the bullpen in the second half haven't been very impressive there. Adam Loewen, Steve Hathaway and Patrick Corbin have combined for 21.2 relief innings at an ERA of 8.72.

Duty now for the future

Right now, it's really hard to figure out what seven men will be in the 2017 bullpen on Opening Day. Maybe we'll re-sign Ziegler, but he's raising his profile and free-agency value nicely, with a 2.12 ERA for the Red Sox since being traded to Boston. Hudson will also be a free-agent, but I can see him likely returning to the fold. Beyond that? Barrett, Burgos, Hathaway as a LOOGY, Godley as long relief, Chafin and Delgado? I can't say it's a roster which exactly fills me with confidence and hope. There may be hope from down on the farm, in the likes of Jimmy Sherfy, though he's not immune to the slump, having an August ERA of 11.57 in eight appearances.

While paying for closers seems an unnecessary waste of resources, I'd not be averse to us looking to strengthen the 'pen with a move for a Ziegler or Clippard type pitcher. By which I mean, someone who is a good reliever, yet who has not been working in the closer's role, getting a large number of recent shiny saves to drive up the price. We'll see what the final month of the season brings, but at this point, the performance has been so bad that you have to consider the bullpen one of, if not the top priority for the front-office this winter.