Diamondbacks’ Secret Weapon : Left-Handed Relief Pitching

Compared to the Diamondbacks, this season the Cubs scored more runs per game and allowed less runs per game. And yet the Diamondbacks won 6 of 7 games against the Cubs. The Diamondbacks had a secret weapon. Left-handed relief pitching. Compared to Cubs left-handed relievers, the Diamondbacks’ left-handed relief pitchers had a better ERA (4.46 vs 5.28) and a better FIP (3.78 vs 4.24).

Let’s look at the left-handed pitchers in the Diamondback’s bullpen.

What are the ERAs and FIPs for the left-handed bullpen pitchers?

Compared to the Diamondbacks right-handed relief pitchers, this season the left handed relief pitchers had a better average ERA (4.46 vs 4.51) and FIP (3.78 vs 4.70).

Let’s look at left-handed relief pitchers last season and this season. If a pitcher left the Diamondbacks, let’s look at how they performed after leaving. The following table compares them. Green shows whether they were better than the Diamondbacks’ averages (2023) for left-handed relief pitchers.

This season through 15 September. Data from Baseball Reference, Diamondbacks’ Average ERA and FIP for left-handed relief pitchers from FanGraphs.

Which left-handed bullpen pitchers get the most strikeouts and whiffs?

Let’s look at last season and this season. Also, a pitcher left the Diamondbacks, let’s look at how they performed after leaving. The following table compares them. Green shows whether they were better than my demarcations.

This season through 15 September. Data from Baseball Reference.

Who are the core left-handed relievers?

In the last two seasons, Kyle Nelson and Joe Mantiply were the Diamondbacks core of left-handed relievers. Although both have a FIP near 4, Kyle Nelson has the better ERA. That better ERA could possibly reflect that this season his deeper statistics are better (SO/BF, whiffs per pitch, and BIP/strike).

Last season Joe Mantiply was an All-Star. I hope he returns to that level soon.

Is Andrew Saalfrank an emerging star?

On 5 September, he pitched for the first time in the Majors. Through 15 September, his ERA (zero) and FIP (1.98) were the best of the Diamondbacks’ left-handed relievers. But star power is measured by more than statistics.

What happened when the pressure was on and the stakes were high? Saturday, he entered the game against the Cubs to start the 10th inning. The game was an epic battle between two teams that wanted to win. This game could decide which team would reach the playoffs. His appearance had a 3.44 average leverage index (Baseball Reference), which was in the top seven for Diamondbacks’ left-handed relievers this season.

He showed he was an emerging star. He completed two full innings (his longest of the season) when the Diamondbacks were almost out of relief pitchers. He allowed zero earned runs (although two unearned runs scored) against a team that ranked 7th in the Majors in runs scored by game. He showed great focus when he fielded two infield balls-in-play by immediately throwing the correct base.

“I am ecstatic for Andrew tonight.” — Andrew Saalfrank’s mom interviewed during his debut at Chase Field.

Was Chafin a good acquisition?

This season, his 4.19 ERA and 3.11 FIP were above Diamondbacks’ average and was better than my demarcations for strikeouts per batter faced (.327 > .250), whiffs per pitch (.155 > .130), and balls-in-play per strike (.218 <.265).

The icing on the cake is that he was traded away for Peter Strzelecki, who has potential to be a better pitcher than Chafin (albeit right-handed), and who is more affordable because he is pre-arb. Playing for the Brewers, Peter Strzelecki’s ERA and FIP slightly slumped this season (ERA 2.83 to 4.54 and FIP 2.84 to 3.79), which may be why he was available. What I like most are his deeper statistics of last season (.270 strikeouts per batter faced, .144 whiffs per pitch, and .235 balls-in-play per strike.

Therefore, Andrew Chafin was a good acquisition and was traded for another good acquisition.

Why has Tyler Holton improved after he was lost on waivers?

To make room for Andrew Chafin, Tyler Holton was put on waivers and lost to the Tigers. That made sense because Holton was only used in low leverage situations and because his fastball velocity was less than 91 MPH. With the Tigers he improved by development of a slider. Although this season it is only 14% of his pitches, it appears that his overall pitching was more effective with his slider. Also, some improvement was due to his one MPH increase in fastball velocity. Also significant was his increased self-confidence.

“The biggest difference is my confidence level,” Holton said. “I was trying to pitch in the big leagues last year. Once I did and had some success, then you start to realize you can pitch in the big leagues. Having the confidence that I belong up here and that I can compete and have success — that mindset change was huge.” — Tyler Holton

Summary.

Although there was significant turnover in left-handed relief pitchers, they pitched very well. Two points:

• They pitched better than the Diamondbacks’ right-handed relief pitchers.
• They pitched better than the Cubs’ left-handed relief pitchers.

Because of the turnover, the overall positive contributions of left-handed relief pitchers could be overlooked. They are the Diamondbacks’ secret weapon.