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What Do Diamondbacks Want in Their Pitchers?

The acquisition of Dan Straily was an insightful outlier.

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Dan Straily pitched for Lotto Giants in KBO.
Dan Straily pitched for Lotto Giants in KBO.
Photo by Han Myung-Gu/Getty Images

Let’s address characteristics that the Diamondbacks look for when they acquire pitchers. Three recently acquired pitchers were: Ian Kennedy, Mark Melancon, and Dan Straily.

Above Average ERA+

These 2022 Diamondbacks had the highest ERA+ in 2021.

  • 175 ERA+ Mark Melancon
  • 174 ERA+ Luis Frias
  • 156 ERA+ Noe Ramerez
  • 136 ERA+ Ian Kennedy
  • 136 ERA+ Tyler Gilbert
  • 126 ERA+ Joe Mantiply
  • 101 ERA+ Merrill Kelly

First, looking at ERA+, it is clear that the Diamondbacks added pitchers with ERA+ well above average (ERA+ of 136 for Kennedy and ERA+ of 175 for Melancon).

An Insightful Outlier

An insightful outlier was the acquisition of Dan Straily. It was more than a low risk minor-league signing.

Dan Straily pitched in the KBO. It’s very unclear whether his ERA+ would have been above average in MLB. Instead, it’s likely his characteristics were the reasons the Diamondbacks signed him.

For Dan Straily, the following four characteristics stood out as desirable – high groundball percentage (54%), high spin (73rd percentile spin on fastball and 80th percentile spin on curve), high strikeout percentage (K% of 23.0%), and low homers per 9 innings (0.65 HR/9).

Eureka! It’s immediately obvious that Melancon shares Staily’s characteristics. And Kennedy shares two characteristics (spin rate and K%).

Although currently Kennedy is a flyball pitcher (his characteristic not shared with Straily), as recently as 2019 his groundball percentage was greater than his flyball percentage (44.4% vs 37.4%). On the other hand, 44.4% only supports ground ball tendencies and is less than the 50% needed to label a pitcher as a groundball pitcher.

J.B. Wendelken shared all 4 characteristics. On 11 August, the Diamondbacks selected J.B Wendelken on waivers. Excluding his partial inning at Coors Field, his 2.89 ERA for the Diamondbacks was outstanding. It’s likely that the opening day bullpen will include J.B Wendelken.

Three additional Diamondbacks pitchers shared 3 characteristics. Six additional Diamondbacks pitchers shared 2 characteristics.

Four Characteristics

The following table shows 12 Diamondbacks pitchers who share at least two characteristics with Straily.

2021 Season. Data from FanGraphs and Baseball Savant.

Groundball tendencies. Two of the three recently acquired pitchers were groundball pitchers. The Diamondbacks want groundball pitchers or pitchers with groundball tendencies. This makes sense for three reasons.

  • Diamondbacks have a reputation for excellent defense. Although 2021 was an exception, it was likely due to promoting players from the minors plus playing in multiple positions.
  • Groundball pitchers allow fewer extra base hits.
  • The average wOBA for groundballs (.220) is less than flyballs (.335) and line drives (.684) per FanGraphs’ library article.

Choosing groundball pitchers is not without risk. About six years ago, there was a debate about whether groundball pitchers were injured more often and whether they had shorter careers. Although the the injury premise was not true (Eno Saris, The Athletic article, November 29, 2021), to my knowledge groundball pitchers having shorter careers remains an open question.

“…It certainly looks like [Bill] James was right: right around 30 years old, ground-ball guys start to age worse. They add four runs to their peak RA/9 two years earlier than the average pitcher. The attrition is much worse, too: between 32 and 34 years old, 34% of all innings pitched leave the game, while 74% of all innings pitched by plus ground-ball pitchers disappear.” — Eno Sarris, FanGraphs article, March 3, 2016

Clearly the Diamondbacks were less-than-greatly concerned with that open question. This offseason, they acquired three older pitchers - Straily at 33, Kennedy at 37, and Melancon who turns 37 next week.

Above average spin rate. Straily, Melancon, and Kennedy have outstanding spin rates. Most of the pitchers in the table had above average spin rates. Clearly the Diamondbacks want fastballs and curves with above average spin. That makes sense because the baseball will have more movement and be less hittable. Albeit Coors field may be an exception because flatter fastballs may be more effective.

Above average strikeout rate. The average K% in the Majors is about 20% per FanGraphs. In the table ten of the 13 pitchers had an above average K%. Ian Kennedy’s 27.2 K% was amazing. The Diamondbacks want an above average strikeout rate. That makes sense for two reasons:

  • Less balls in play means less runs scored against the Diamondbacks.
  • A high rate of strikeouts generally means that the Diamondback pitcher is in control of the at-bats.

Low homers per 9 innings. About half the pitcher had less than one homer per 9 innings. This is a desired characteristic. Although homers in 2021 were not a record high, there is a general trend of more homers every season. Perhaps the deadened baseball will reduce homers in 2022.

Because homers make a high impact, some batters sacrifice hit percentage to increase their homers. When Diamondback pitchers keep homers low, it increases winning chances.


When the Diamondbacks acquire a pitcher, they want a groundball pitcher, whose fastball and curve have an above average spin rate, whose strikeout percentage is above average, and who allows few homers.

“All truths are easy to understand once they are discovered; the point is to discover them.” — Galileo Galilei