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Why Lucas Giolito is a Possible Acquisition for the Diamondbacks

I’m optimistic about his pitching performance next season.

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Lucas Giolita.
Lucas Giolito.
Photo by Duane Burleson/Getty Images

Two stories explain last season.

One story was as good as expected, and one story was worse than expected.

His first story was a successful bounce back story.

It started at the beginning of the season and ended on 26 July when the White Sox traded him. A long time player for the White Sox (since December 2016), his pitching was well above average every season, except 2018 and 2022.

In this story, he bounced back from 2022. His ERA improved from 4.90 to 3.70. His BA, OBP, SLG, and wOBA all improved.

Two warning flags were his expected SLG (xSLG) got worse (from .397 to .441) and his Home Runs per 9 Innings (HR9) got worse (from 1.34 to 1.49). In the context of his bounce back, the flags might have been random noise.

Perhaps all good things come to an end. In any case his time as a White Sox ended abruptly.

His second story was he pitched badly for the Angels and the Guardians.

The story started with pitching for the Angels. When the Angel’s fell out of contention, the Angels waived him and the Guardians claimed him.

Playing for those two teams, his ERA, SLG, and wOBA were at career worsts. His HR9 doubled from 1.49 to 2.98.

As the season ended, he became a free agent.

Why did his pitching slump?

The important question is, “What happened?” Let’s look at four possibilities (bad defense, bad luck, disruption of his pitching routine, and pitching mechanics).

He suffered from his teams’ bad defense.

During the second story’s 12 starts, he experienced 6 unearned runs due to defensive errors. Half an unearned run per start is a significant indicator of poor defense.

Based on a comparison of his expected ERA (xERA) and actual ERA, I estimated that during the second story, poor defense accounted for about 2 earned runs.

Because the Diamondbacks’ DRS was ranked as the 4th best in the Majors (compared to the White Sox who ranked 29th best), I am confident that Lucas Giolito would have better results if he pitched for the Diamondbacks.

His luck was bad.

The following two facts, when they both happen at the same time, strongly suggest that Lucas Giolito had bad luck.

  • His actual results (BA, OBP, SLG, and wOBA) were worse than his expected results (xBA, xOBP, xSLG, and xwOBA).
  • Except for his expected batting average (xBA), which improved by 3%, his other expected stats (xOBP, xSLG, and xwOBA) all worsened between 2 and 3%, which is a very small amount. That small change contrasts with the big change in his actual statistics, which worsened by between 9% and 34%.

I am confident that next season his pitching results will bounce back because luck that bad is not sustainable.

His pitching routine was disrupted.

Pitching every fifth day is a routine that pitchers build around. When his second story started, he stayed at every fifth day for two games. After the first two games, in the 10 remaining games, each of his starts happened after a different number of rest days than his previous start. His routines must have been continuously disrupted.

And his first two games were disruptive, too. He changed to a different team. And his first game was in Toronto Canada and the second game was in Atlanta Georgia. More than just the travel, the temperatures at game time were widely different. His start before Toronto was at 85 degrees Fahrenheit and rose a few degrees during the game. The Toronto start was at 77 degrees Fahrenheit and fell a couple degrees during the game. The Atlanta start was at 86 degrees and rose 4 degrees during the game. Temperature data from the Underground Weather website.

His pitching mechanics drifted away from optimal.

Although mechanics are not the answer to everything, the following quote seems to indicate that the Diamondbacks’ pitching coaches could help Lucas Giolito adjust his mechanics. That adjustment would contribute to his bounce back.

“…He seemed to lose his release point on his slider later in the year, and his fastball command was probably the worst it’s been since he revamped his arm action before the 2019 season. His slider has fallen off by every metric over the past two seasons, going from 5.3 inches of total movement and 28 percent active spin two years ago to just 3.3 inches and 17 percent this past season, while his arm slot and thus the observed movement on the pitch have drifted upwards. His fastball is as hard as ever, but it’s down 200 RPMs from 2021 (as is the slider) and has lost almost an inch of horizontal break … which might be part of why he allowed 19 homers on the pitch last year, along with hard contact half the time hitters put it in play.” — Keith Law

Next Season.

Reasons to be optimistic about his performance follow:

  • Marcel the Monkey (Baseball Reference) projected 2024 ERA of 4.66 and HR9 of 1.6.
  • Steamer (FanGraphs) projected 2024 ERA of 4.31 and HR9 of 1.38.
  • In his first story, more than half his starts were quality starts (11 of 21 starts were 6+innings with 3 or less earned runs).
  • His pitching looked great in view of three of my preferred stats. Those stats were great in his first story and his second story.

The following table shows his pitching was consistently great in terms of strikeouts per batter faced (SO/BF), whiffs per pitch, and balls in play per strike (BIP/strike):

Data from Baseball Reference.

Lucas Giolito is a fit with the Diamondbacks.

He always follows his game plan.

As you likely know, the Diamondbacks place great importance in their game plans. Lucas Giolito always follows his team’s game plan per the following quote:

“And he’s a guy, from what I understand, follows a game plan perfectly. If you have a bad game plan, he’ll execute it, but it won’t go well.” — David Vassegh

His mental approach to baseball.

Lucas Giolito was asked about why the White Sox fell out of contention. His answer (see quote) reflects that he knew a mental key to how the White Sox could have stopped losing, but did not. Knowing that key reflects one aspect of his above-average mental approach to baseball.

“We couldn’t find ways to pick each other up when we needed to, and it led to a lot of losing, and when you’re losing a lot now the vibes are going down down down down. It’s hard to be like, ‘all right guys now we’re going to turn this around,’ it was hard to get that kind of energy going.” — Lucas Giolito

He has a similarity to a past Diamondbacks’ pitcher.

This season, he shares something in common with former Diamondback Robbie Ray. Each pitcher had a 6-game span with exactly 6 unearned runs allowed and exactly 45 strikeouts. Giolito’s was 22 August to 20 September of this season. Ray’s was 3 May to 29 May of 2019.

Giolito was the only pitcher this season to have a six game span with at least 6 unearned runs and at least 45 strikeouts per Baseball Reference.


This season, after a successful bounce back with the White Sox, Lucas Giolito pitched badly for the Angels and Guardians. The likely causes were poor defense, bad luck, disruption of his routines, and drift of his pitching mechanics. Despite those problems, his pitching was consistently great in terms of strikeouts per batter faced, whiffs per pitch, and balls-in-play per strike.

Next season, there are reasons for optimism - two projections, last season’s quality starts, and his consistency in my three preferred statistics.

He would be a good fit for the Diamondbacks because he always follows his game plan, his above-average mental approach, and his similarity for former Diamondback Robbie Ray.