Triggered by hotclaws's comment, I thought it might be interesting to look at how the team's relievers have performed down the years. So, here's a chart comparing the Diamondbacks' bullpen ERA against the National League average, along with our top reliever or relievers (as measured by bWAR) for each season. Obviously, this covers the offensive boom of the early two thousands, as well as the much more pitcher-friendly seasons lately, so I've also included a percentage column. This is our ERA compared to the NL average ERA, so the higher that is, the worse for us.
|YEAR||ARI||NL||%||Top performer, bWAR|
|1998||4.80||3.99||120.30||Gregg Olson, 1.4|
|1999||3.77||4.39||85.88||Greg Swindell, 2.0|
|2000||4.37||4.56||95.83||Greg Swindell, 1.7|
|2001||3.88||4.12||94.17||Byung-Hyun Kim, 3.1|
|2002||4.60||3.84||119.79||Byung-Hyun Kim, 4.1|
|2003||3.62||4.06||89.16||Oscar Villarreal, 2.2|
|2004||4.69||4.09||114.67||Mike Koplove, 1.1|
|2005||5.50||4.23||130.02||Jose Valverde, 2.0|
|2006||4.36||4.19||104.06||Luis Vizcaino, 1.4|
|2007||3.95||4.08||96.81||Jose Valverde, 2.2|
|2008||4.09||4.09||100.00||Chad Qualls, 1.8|
|2009||4.61||4.00||115.25||Chad Qualls/Juan Gutierrez, 0.7|
|2010||5.74||3.97||144.58||Mike Hampton, 0.3|
|2011||3.71||3.59||103.34||J.J. Putz, 1.6|
|2012||3.28||3.77||87.00||Brad Ziegler/David Hernandez, 1.7|
|2013||3.52||3.50||100.57||Brad Ziegler, 1.7|
|2014||3.92||3.53||111.05||Evan Marshall, 0.9|
A couple of things to mention. With our figure not being park-adjusted, it's hardly a surprise that we've been worse than average more often than not (10 times in 17 years). However, since we're looking to compare locally, year to year, park effects should be the same - it's not like we're the Padres or Rockies, tinkering endlessly with fences and humidors to get an edge. It also goes to show how much things have changed. the Diamondbacks' above-average ERA of 4.37 in 2000, would have put them ahead only of Colorado in the National League this season. It has become a lot harder to score against bullpens: ERAs have dropped almost three-quarters of a run since 2005.
However, I doubt anyone who remembers the 2010 bullpen will be casting too many aspersions at the 2015 version, being painfully aware of how bad things can actually be. For context, our "leading performer" Mike Hampton, threw precisely 4.1 innings. That they were scoreless, was enough to make him easily our best reliever, since the only other bullpen arm that year to have a positive bWAR, was Carlos Rosa. This has likely been the first time since 2010 that anyone has mentioned Carlos Rosa. The overall 5.74 ERA is the highest posted by a team in the National League, since the 1938 Phillies bullpen had a 6.16 ERA, and they threw 150 innings less.
On that basis, Kevin Towers does deserve credit for getting things back under control. A couple years later, our bullpen ERA was almost two and a half runs better, and that 87% of league average remains the lowest mark for us since 1999. However, as shoewizard pointed out, the figures for Arizona over the first four years of the Josh Byrnes era (which does conveniently exclude the 2010 gurgling vortex of suck) are fairly comparable to the first four years of the Kevin Towers era. Certainly, Dave Stewart inherits a better set of arms than his predecessors, an 111% ERA well below the 130% and 145% bequeathed to Byrnes and Towers respectively.
Here's the main data in pictorial format, for those who prefer graphs to tables. It should quite nicely the wild swings in output from the Arizona bullpen, and also the steady decline in bullpen ERA over the last fifteen or so years.
This probably means little or nothing for the 2015 bullpen, which will have at most only three survivors from the eight men who opened the 2014 campaign there: Addison Reed, Oliver Perez and, health permitting, Brad Ziegler. Such is the nature of relievers: a volatile bunch for the most, in part because 60 innings is a small enough sample size that random variation will have much more effect than over the 200 innings of work a starting pitcher gets. If you look at the four top bullpens by ERA in the NL last year - Padres, Nationals, Giants and Mets - none were in the top four for 2013.
Fan perception of a bullpen is also always going to be skewed, because their successes, particularly outside of the closer, are so much more understated than those of position players. Posting a zero is never going to make as much of an impression as driving in a run. Offensive failure is always the standard in baseball, so a reliever can never do better than enforcing that standard. The best bullpen is, I suspect, the one you never notice! So, here's to not noticing the Arizona Diamondbacks relievers very much in 2015...