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Have Diamondback Starters Pitched Above Average?

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Each start can be measured with a single number called game score.

Gallen after his 79.3 Game Score.
Gallen after his 79.3 Game Score.
Photo by Todd Kirkland/Getty Images

The Approach

Game score was originally developed by Bill James. It was designed to have an average of 50. It was good and can be found at Baseball Reference. Tango Tiger tweaked it into the version provided on the FanGraph site. Then 538.com tweaked it into a version that they use in their model to predict the odds for each game.

Three versions of Game Score (there may be more) can be found at Baseball Reference, FanGraphs, and 538.com. When we look at Diamondback starters, we will average the three game scores.

What are the most significant differences?

  • Baseball Reference definition. Walks have less impact. Three differences that are unlike Fangraphs and 538.com: it treats ER and unER differently, homers are not worth extra, and extra points for completed innings after the fourth inning.
  • Fangraphs and 538.com’s definitions are fairly similar, with two differences: FanGraphs has more impact from homers and outs.

The following chart shows the formulas (used by the three websites).

Baseball Reference, FanGraphs, and 538.com.

After finding the average (of the three versions) game score for each starter’s season, then we will look at two questions.

  • What percent of his above average starts were spoiled by his team? Neil Paine defined a spoiled start as game score above 60 and offense scored 2 or less runs in the game. By that definition it only happened once, to Taylor Widener on 16 April (games through 6 May).
  • What percentage of his starts were so bad that they could be described as batting practice starts? Let’s define a batting practice start as average (of the three versions) game score below 40 and innings pitched less than 5. (Poor games with 5+ innings qualify as innings eater starts, which at least saves the bullpen from overwork.)

The Numbers

The following chart shows this season’s average game scores (Baseball Reference, FanGraphs, and 538.com) for each Diamondback pitcher who has started a game through 6 May.

Data from Baseball Reference, Game Score Formulas from Baseball Reference, FanGraphs, and 538.com.

The average of the three game scores showed the pitchers ranked as follows:

  • 58.3 Zac Gallen
  • 53.9 Taylor Widener
  • 52.3 Madison Bumgarner
  • 46.0 Riley Smith
  • 45.3 Luke Weaver
  • 44.1 Merrill Kelly
  • 31.6 Caleb Smith

The best starts of the season, based on Game Score above 60, follow:

  • 85.6 Madison Bumgarner, 25 April
  • 83.0 Luke Weaver, 11 April
  • 79.3 Zac Gallen, 25 April
  • 69.8 Madison Bumgarner, 6 May
  • 67.5 Taylor Widener 4 April
  • 65.1 Taylor Widener, 16 April
  • 63.8 Merrill Kelly, 27 April
  • 61.3 Madison Bumgarner, 30 April
  • 61.0 Madison Bumgarner, 18 April

Two starts were spoiled by Neil Paine’s definition. That was 6.5% of the first 31 starts.

Six starts were batting practice starts by our newly coined definition. That was 19.4% of the first 31 starts.

The Opinions

Interestingly, when starters pitched an above average game (Game Score above 50), the Diamondbacks winning percentage was 75% (9 games out of 12). What about the three losses? Two were spoiled starts by Taylor Widener and Madison Bumgarner, and one was a Zac Gallen’s game.

It’s clear that Madison Bumgarner started the season pitching poorly and then improved greatly. With game score we have a way to measure how much better he is pitching now.

Although he may be past his prime, the Diamondbacks paid big buck to sign Madison Bumgarner because they had high expectations for his pitching. That’s why his first three starts, with game scores ranging from 23.5 to 36.3, well below the average of about 50, were alarming. Two of his first three starts were bad enough to qualify for our newly minted definition of batting practice starts. Something changed.

After that change it was lights out pitching. His next four game scores were all above 60. Most impressive was his 85.6 game score on 25 April against the Braves, which is the highest of any Diamondback this season. His game on 6 May was great and met the requirements to be designated a spoiled start. Bumgarner credited the “mental side” for his improved pitching. He said that maybe down the road he will divulge how he went about it. I look forward to it!

Luke Weaver’s start on 3 May was disappointing; his game score was 30.5. Afterwards, he said words like frustrating and unbearable to describe that game. His game score of 33.5 on 17 April was similar. However, there is reason to be optimistic – his 83 game score on 11 April against the Reds. Luke Weaver is close to achieving an average to good season. As he said, “It’s just a teeny little, minor adjustment from going out and putting up at least six innings and minimal runs and having a chance to win the game.”

Luke Weaver isn’t the only Diamondback starter with low game scores – Bumgarner had two (23.5 and 28.8), Kelly had two (30.5 and 32.1), and Celeb Smith had one (31.6). The average game scores for Luke Weaver, Merrill Kelly, and Riley Smith are about the same (45.3, 44.1, and 46.0 through 6 May). Interestingly, their ERA+s are similar (69, 72, and 86 through 6 May). At this point in the season, their potentials are equal. However, the deciding factor could be their innings pitched in 2019/2020 (116.1, 214.2, and 152.1). Luke Weaver will likely hit his season’s pitch limit soonest, followed by Riley Smith.

After his injury, Gallen started the season on 13 April. It was a good start (game score of 55.1), but the Diamondbacks lost. Zac Gallen pitched 4 innings and left the game with the Diamondbacks leading 5-1, which gave the Diamondbacks winning chances.

Zac Gallen’s season average Game Score of 58.3 (through 6 May) is the highest on the Diamondbacks. Most impressive was his 79.3 game score on 25 April against the Braves, which was the third highest of any Diamondback this season. During the remainder of the season, he and Madison Bumgarner will likely be challenging each other for ace status. I look forward to that friendly competition.

The Answer

Yes. Through 10 May, 42.9% (15 of 35) of starts were above average. One game had a game score of 50 (average). The good news is that the percentage of above average starts will likely rise during the remainder of the season for three reasons:

  • Madison Bumgarner has found his groove.
  • Luke Weaver is just a small adjustment away from his best. On 10 May, his scoreless start was a sign he may have done found the adjustments he needed.
  • Zac Gallen is back from his preseason injury.